refactor(electron): remove the configuration-preset system and read .env with dotenv

- delete electron/settings, the settings preload and window, the
  config-presets IPC channels, the Configuration menu and the preset
  watcher in scripts/electron-dev.mjs; config-manager.ts keeps only the
  user locale (still read from config-presets.json so the saved
  language survives)
- electron/main/env-loader.ts parses .env with dotenv instead of a
  hand-written parser; electron:compile bundles dependencies
- drop the unreachable development branches in port-manager.ts and
  next-server.ts, the duplicated locale normalisation in menu-i18n.ts,
  the unused electronAPI members, resources/entitlements.mac.plist
- scripts/copy-dereferenced.cjs shared by afterPack and
  prepare-electron-build
- CI: delete ci.yml, move type check and concurrency into test.yml,
  Node 24 everywhere, docker-build only on main
- remove unused dependencies (@xmldom/xmldom, remark-gfm,
  @anthropic-ai/tokenizer, @testing-library/user-event, concurrently,
  wait-on, eslint, eslint-config-next, @vitest/coverage-v8, shx),
  .eslintrc.json and the vitest coverage block

scripts/afterPack.cjs

@@ -4,49 +4,10 @@
  * and ad-hoc signs macOS apps for offline draw.io bundle compatibility
  */
 
-const {
-    copyFileSync,
-    existsSync,
-    lstatSync,
-    mkdirSync,
-    readdirSync,
-    statSync,
-} = require("fs")
+const { existsSync } = require("fs")
 const path = require("path")
 const { execSync } = require("child_process")
-
-/**
- * Copy directory recursively, converting symlinks to regular files/directories.
- * This is needed because cpSync with dereference:true does NOT convert symlinks.
- * macOS codesign fails if bundle contains symlinks pointing outside the bundle.
- */
-function copyDereferenced(src, dst) {
-    const lstat = lstatSync(src)
-
-    if (lstat.isSymbolicLink()) {
-        // Follow symlink and check what it points to
-        const stat = statSync(src)
-        if (stat.isDirectory()) {
-            // Symlink to directory: recursively copy the directory contents
-            mkdirSync(dst, { recursive: true })
-            for (const entry of readdirSync(src)) {
-                copyDereferenced(path.join(src, entry), path.join(dst, entry))
-            }
-        } else {
-            // Symlink to file: copy the actual file content
-            mkdirSync(path.join(dst, ".."), { recursive: true })
-            copyFileSync(src, dst)
-        }
-    } else if (lstat.isDirectory()) {
-        mkdirSync(dst, { recursive: true })
-        for (const entry of readdirSync(src)) {
-            copyDereferenced(path.join(src, entry), path.join(dst, entry))
-        }
-    } else {
-        mkdirSync(path.join(dst, ".."), { recursive: true })
-        copyFileSync(src, dst)
-    }
-}
+const copyDereferenced = require("./copy-dereferenced.cjs")
 
 module.exports = async (context) => {
     const appOutDir = context.appOutDir