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

.github/workflows/test.yml

@@ -6,6 +6,13 @@ on:
   push:
     branches: [main]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
 jobs:
   lint-and-unit:
     name: Lint & Unit Tests
@@ -16,12 +23,15 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v6
         with:
-          node-version: "20"
+          node-version: "24"
           cache: "npm"
 
       - name: Install dependencies
         run: npm ci
 
+      - name: Type check
+        run: npx tsc --noEmit
+
       - name: Run lint
         run: npm run check
 
@@ -57,7 +67,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v6
         with:
-          node-version: "20"
+          node-version: "24"
           cache: "npm"
 
       - name: Install dependencies