Productivity features, UI translations, local email translation

- Snooze (with a Snoozed folder), keyboard shortcuts with a Settings
  section, mail templates (Compose > More > Templates), a Subscriptions
  folder with bulk unsubscribe/delete, and tracker blocking with a
  Privacy toggle (on by default)
- Own dialogs instead of browser popups; emoji picker in compose; compose
  windows survive a visit to Settings
- Sentence completion learned from the user's sent mail (no AI)
- Interface in English and Polish (one file per language, English as the
  fallback), picked from the browser on first run, then kept
- Email translation on the server via LibreTranslate: Translate button
  and "Translate to...", messages in several languages translated part
  by part, names/addresses/emoji/file names/phone numbers kept, an
  animated line while translating
- Antispam "Mark as spam" loads with the message, not when the menu opens

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/package-lock.json

@@ -8,9 +8,11 @@
       "name": "webmail-frontend",
       "version": "0.1.0",
       "dependencies": {
+        "@emoji-mart/data": "~1.2.1",
         "@tanstack/react-query": "~5.51.0",
         "@tanstack/react-virtual": "~3.8.0",
         "docx-preview": "^0.4.0",
+        "emoji-mart": "~5.6.0",
         "jszip": "^3.10.1",
         "pdfjs-dist": "^4.10.38",
         "qrcode.react": "~4.1.0",
@@ -524,6 +526,12 @@
         "node": ">=18"
       }
     },
+    "node_modules/@emoji-mart/data": {
+      "version": "1.2.1",
+      "resolved": "https://registry.npmjs.org/@emoji-mart/data/-/data-1.2.1.tgz",
+      "integrity": "sha512-no2pQMWiBy6gpBEiqGeU77/bFejDqUTRY7KX+0+iur13op3bqUsXdnwoZs6Xb1zbv0gAj5VvS1PWoUUckSr5Dw==",
+      "license": "MIT"
+    },
     "node_modules/@esbuild/aix-ppc64": {
       "version": "0.21.5",
       "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.21.5.tgz",
@@ -3457,6 +3465,12 @@
       "dev": true,
       "license": "ISC"
     },
+    "node_modules/emoji-mart": {
+      "version": "5.6.0",
+      "resolved": "https://registry.npmjs.org/emoji-mart/-/emoji-mart-5.6.0.tgz",
+      "integrity": "sha512-eJp3QRe79pjwa+duv+n7+5YsNhRcMl812EcFVwrnRvYKoNPoQb5qxU8DG6Bgwji0akHdp6D4Ln6tYLG58MFSow==",
+      "license": "MIT"
+    },
     "node_modules/end-of-stream": {
       "version": "1.4.5",
       "resolved": "https://registry.npmjs.org/end-of-stream/-/end-of-stream-1.4.5.tgz",