chore: remove unused deps, pin toolchain, single-source version, quarantine e2e

- Uninstall zustand, tailwindcss, autoprefixer, tweetnacl-util (all
  unused); README no longer advertises Tailwind/Zustand.
- Fix stale 'Tone' -> 'Explain' copy in Options.
- Add .nvmrc/engines/packageManager (Node 22 to match CI).
- wxt.config.ts reads manifest version from package.json so the two
  can never drift.
- Ignore *.zip build artifacts.
- Skip the two e2e specs with literal [EXTENSION_ID] placeholders
  (cannot pass; TODO references the e2e-ID-resolution task).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tsconfig.json

@@ -10,6 +10,7 @@
     "skipLibCheck": true,
     "types": ["chrome"],
     "esModuleInterop": true,
+    "resolveJsonModule": true,
     "allowImportingTsExtensions": true,
     "paths": {
       "~/*": ["./src/*"]