feat: add persistent dictionary selection

[zefutoff]

Summary

• add persistent dictionary selection
• support all variants, classic orthography and 1990 reform dictionaries
• switch the active Grammalecte dictionary without recreating the QuickJS runtime
• clear morphology storage when changing dictionaries
• share the selected dictionary across SpellCheckerService, PROCESS_TEXT and the IME
• add dictionary selection to the existing correction settings screen
• preserve the selected dictionary across app restarts
• add real-engine and Android instrumentation coverage
• mark dictionary choice complete in the roadmap

Validation

• make check
• make assemble
• git diff --check
• JavaScript bridge contract tests
• real QuickJS engine tests for all three bundled dictionaries
• Android instrumentation on API 26
• Android instrumentation on Samsung Galaxy S21 / Android 15
• verified dynamic dictionary refresh on an already-running engine
• verified on physical device:
  • all variants accepts coût and cout
  • classic accepts coût and rejects cout
  • 1990 reform accepts cout and rejects coût
• verified dictionary selection persists
• final APK still requests no INTERNET permission