refactor: remove dead code and over-engineering found by two audits (#986)

## Problem

Two audits of the repository (a workflow of finder, dedup and per-file verifier agents, run on 2026-10-11 against 1f4141e and again against 07f3e3c after a first round of refactoring) found dead code and features that were more machinery than the app needs: an Electron configuration-preset system with its own settings window, three copies of the about page, a hand-written `.env` parser, an "extended" system prompt nobody selected, two data migrations for formats from 2025-12 and 2026-01, a server-side example cache, type-to-confirm provider deletion, 81 unused dictionary keys, wrapper components around single call sites, and a long tail of unused exports, props, options and tests.

## Change

Every item below was either approved one by one or covered by "fix all of the others".

- **Electron:** the configuration-preset system is gone (settings window, preload, IPC, menu entry, dev watcher); `config-manager.ts` keeps only `userLocale`; `.env` files are parsed with `dotenv`. Entitlements file and a duplicate CI workflow removed; `test.yml` gets a type check and concurrency.
- **Server:** no extended prompt, no example cache, no `ENABLE_HISTORY_XML_REPLACE`, no message metadata or `hasConfig`; the connection test is one shared helper; EdgeOne loses its mock branch and model aliases; `DEBUG_LLM_PAYLOAD` logs message structure instead of payloads; Langfuse scoring helper; `apiKeyEnv` arrays kept and documented in `env.example` and the provider docs.
- **Pages:** one about page per language from a single component (old `/cn` and `/ja` URLs redirect with 308); layout uses `hasLocale`; the GitHub icon is a local component instead of `react-icons`; Cloudflare deploys without an R2 cache by default.
- **Chat and canvas:** the legacy `diagramHistory` conversion, the localStorage chat migration and the templates storage are gone; `chat-engine` reads the diagram through the context's refs; the diagram context has one tagged export path (`requestTaggedExport` / `fetchDiagramXml`); the screenshot check uses fetch + JSON and `generateText` with `Output.object`; `load-diagram` accepts `<svg:svg>` and strips the XML prolog.
- **Settings UI:** `model-selector` inlines its Dialog, Command and Tooltip; `ai-elements/model-selector`, `button-with-tooltip`, `error-toast` removed; no type-to-confirm, no footer, no `bedrockApiKey`; `use-model-config` loses the old-format migration; one reasoning component; the shimmer is CSS (no `motion`, no `@radix-ui/react-use-controllable-state`); 81 dictionary keys removed in all four languages.
- **MCP server:** `registerTool` / `ok` / `fail` replace per-tool try/catch; `syncFromBrowser`, `commitDocument`, `describePages`; the hand-written XML syntax check, unused result fields, `pickPageSelector`, `expandStyles` and the `host` attribute handling are gone; tests get a shared `setup.ts` and drive the server through the SDK client.
- **Prompt:** the web app's style rules come from the MCP drawing guide (`styleRules`), byte-identical to before.
- **Tests:** shared e2e helpers (`openApp`, `sse`, `toolCallEvents`, `chunkedReplies`); placeholder specs dropped; `settings-review-fixes` split by topic; unit tests use `vi.stubEnv`.
- **Dependencies removed:** `@xmldom/xmldom`, `remark-gfm`, `@anthropic-ai/tokenizer`, `@testing-library/user-event`, `concurrently`, `wait-on`, `eslint`, `eslint-config-next`, `@vitest/coverage-v8`, `shx`, `motion`, `@radix-ui/react-use-controllable-state`, `react-icons`.

Source lines: 74,983 before, 67,418 after (excluding lockfiles).

The last commit merges #984 (the canvas shell). Where the shell, the classic page or their tests depend on a wire format or signature this branch had changed, main's version wins (export fields of the poll response, `addHistory` signature); where main only extended code this branch restructured, main's change is carried into the new structure (`start_session`, `get_selection`, `prepareNewDiagram`, the diagram context's `requestExport`).

## Testing

- `tsc --noEmit` for the web app, `packages/mcp-server`, its shell and `electron`: clean
- `biome ci`: 0 errors (37 pre-existing warnings)
- Root `vitest run`: 719 passed; `packages/mcp-server` `vitest run`: 372 passed
- `next build`: clean
- Playwright, whole web suite on the dev server (4 workers): 280 tests, 279 passed; `language.spec.ts` "a stale offer to switch without saving does nothing once a message is being sent" failed under parallel load and passed alone, as it does on main

edge-functions/api/edgeai/chat/completions.ts

@@ -29,6 +29,7 @@ const messageItemSchema = z
     })
     .passthrough()
 
+// The fields read here; every other field is passed on to AI.chatCompletions
 const messageSchema = z
     .object({
         messages: z.array(messageItemSchema),
@@ -36,21 +37,6 @@ const messageSchema = z
         stream: z.boolean().optional(),
         tools: z.any().optional(),
         tool_choice: z.any().optional(),
-        functions: z.any().optional(),
-        function_call: z.any().optional(),
-        temperature: z.number().optional(),
-        top_p: z.number().optional(),
-        max_tokens: z.number().optional(),
-        presence_penalty: z.number().optional(),
-        frequency_penalty: z.number().optional(),
-        stop: z.union([z.string(), z.array(z.string())]).optional(),
-        response_format: z.any().optional(),
-        seed: z.number().optional(),
-        user: z.string().optional(),
-        n: z.number().int().optional(),
-        logit_bias: z.record(z.string(), z.number()).optional(),
-        parallel_tool_calls: z.boolean().optional(),
-        stream_options: z.any().optional(),
     })
     .passthrough()
 
@@ -61,12 +47,6 @@ const ALLOWED_MODELS = [
     "@tx/deepseek-ai/deepseek-v3-0324",
 ]
 
-const MODEL_ALIASES: Record<string, string> = {
-    "deepseek-v3.2": "@tx/deepseek-ai/deepseek-v32",
-    "deepseek-r1-0528": "@tx/deepseek-ai/deepseek-r1-0528",
-    "deepseek-v3-0324": "@tx/deepseek-ai/deepseek-v3-0324",
-}
-
 /**
  * Create standardized JSON response
  */
@@ -145,8 +125,16 @@ export async function onRequest({ request, env }: any) {
             )
         }
 
-        const { messages, model, stream, tools, tool_choice, ...extraParams } =
-            parseResult.data
+        // stream is taken out so it is not passed on: AI.chatCompletions
+        // only streams, and every caller reads a stream
+        const {
+            messages,
+            model,
+            stream: _,
+            tools,
+            tool_choice,
+            ...extraParams
+        } = parseResult.data
 
         // Validate messages
         const userMessages = messages.filter(
@@ -165,14 +153,13 @@ export async function onRequest({ request, env }: any) {
         }
 
         // Resolve model
-        const requestedModel = model || ALLOWED_MODELS[0]
-        const selectedModel = MODEL_ALIASES[requestedModel] || requestedModel
+        const selectedModel = model || ALLOWED_MODELS[0]
 
         if (!ALLOWED_MODELS.includes(selectedModel)) {
             return createResponse(
                 {
                     error: {
-                        message: `Invalid model: ${requestedModel}.`,
+                        message: `Invalid model: ${selectedModel}.`,
                         type: "invalid_request_error",
                     },
                 },
@@ -181,39 +168,10 @@ export async function onRequest({ request, env }: any) {
         }
 
         console.log(
-            `[EdgeOne] Model: ${selectedModel}, Tools: ${tools?.length || 0}, Stream: ${stream ?? true}`,
+            `[EdgeOne] Model: ${selectedModel}, Tools: ${tools?.length || 0}`,
         )
 
         try {
-            const isStream = !!stream
-
-            // Non-streaming: return mock response for validation
-            // AI.chatCompletions doesn't support non-streaming mode
-            if (!isStream) {
-                const mockResponse = {
-                    id: `chatcmpl-${Date.now()}`,
-                    object: "chat.completion",
-                    created: Math.floor(Date.now() / 1000),
-                    model: selectedModel,
-                    choices: [
-                        {
-                            index: 0,
-                            message: {
-                                role: "assistant",
-                                content: "OK",
-                            },
-                            finish_reason: "stop",
-                        },
-                    ],
-                    usage: {
-                        prompt_tokens: 10,
-                        completion_tokens: 1,
-                        total_tokens: 11,
-                    },
-                }
-                return createResponse(mockResponse)
-            }
-
             // Build AI.chatCompletions options for streaming
             const aiOptions: any = {
                 ...extraParams,