[Feature] Server-side multi-provider/model support (#583)

* [Feature] Server side multi-pvorider/model support

* copilot suggesition implemented

* feat: improve model selector UI and auto-select default server model

- Replace emoji headers with Lucide icons (Monitor, User)
- Fix transition-all to explicit properties per web guidelines
- Use CSS padding instead of hardcoded space indentation
- Add ModelSelectorSectionHeader component for section headers
- Replace Star icon with "default" text label
- Style Configure button with muted text color
- Auto-select default server model when page loads
- Support AI_MODELS_CONFIG env var for cloud deployments
- Support custom apiKeyEnv/baseUrlEnv per provider config

* docs: update server-side multi-model configuration documentation

- Add AI_MODELS_CONFIG env var option for cloud deployments
- Document apiKeyEnv and baseUrlEnv fields for custom env var names
- Document default field for auto-selecting default model
- Remove deprecated version field from examples
- Add field reference table for clarity

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

tests/unit/server-model-config.test.ts

@@ -0,0 +1,85 @@
+import { afterEach, describe, expect, it } from "vitest"
+import {
+    loadFlattenedServerModels,
+    type ServerModelsConfig,
+    ServerModelsConfigSchema,
+} from "@/lib/server-model-config"
+
+const ORIGINAL_ENV = { ...process.env }
+
+afterEach(() => {
+    process.env.AI_PROVIDER = ORIGINAL_ENV.AI_PROVIDER
+    process.env.AI_MODEL = ORIGINAL_ENV.AI_MODEL
+    process.env.AI_MODELS_CONFIG_PATH = ORIGINAL_ENV.AI_MODELS_CONFIG_PATH
+    process.env.AI_MODELS_CONFIG = ORIGINAL_ENV.AI_MODELS_CONFIG
+})
+
+describe("ServerModelsConfigSchema", () => {
+    it("accepts valid provider names", () => {
+        const config: ServerModelsConfig = {
+            providers: [
+                {
+                    name: "OpenAI Server",
+                    provider: "openai",
+                    models: ["gpt-4o"],
+                },
+            ],
+        }
+
+        expect(() => ServerModelsConfigSchema.parse(config)).not.toThrow()
+    })
+
+    it("rejects invalid provider names", () => {
+        const invalidConfig = {
+            providers: [
+                {
+                    name: "Invalid Provider",
+                    // Cast to any so we can verify runtime validation, not TypeScript
+                    provider: "invalid-provider" as any,
+                    models: ["model-1"],
+                },
+            ],
+        }
+
+        expect(() =>
+            ServerModelsConfigSchema.parse(invalidConfig as any),
+        ).toThrow()
+    })
+})
+
+describe("loadFlattenedServerModels", () => {
+    it("returns empty array when config file is missing", async () => {
+        // Point to a non-existent config path so fs.readFile throws ENOENT
+        process.env.AI_MODELS_CONFIG_PATH = `non-existent-config-${Date.now()}.json`
+
+        const models = await loadFlattenedServerModels()
+        expect(models).toEqual([])
+    })
+
+    it("flattens providers and marks default model from env var config", async () => {
+        // Use AI_MODELS_CONFIG env var instead of file
+        const config: ServerModelsConfig = {
+            providers: [
+                {
+                    name: "OpenAI Server",
+                    provider: "openai",
+                    models: ["gpt-4o", "gpt-4o-mini"],
+                    default: true,
+                },
+            ],
+        }
+        process.env.AI_MODELS_CONFIG = JSON.stringify(config)
+        process.env.AI_MODELS_CONFIG_PATH = "" // Clear file path
+
+        const models = await loadFlattenedServerModels()
+
+        expect(models.length).toBe(2)
+
+        const defaults = models.filter((m) => m.isDefault)
+        expect(defaults.length).toBe(1)
+
+        const defaultModel = defaults[0]
+        expect(defaultModel.provider).toBe("openai")
+        expect(defaultModel.modelId).toBe("gpt-4o") // First model of default provider
+    })
+})