feat: add personal dictionary

[zefutoff]

Summary

• add a persistent personal dictionary
• build a real Graphspell dictionary in memory with Grammalecte DAWG
• support adding, listing and removing personal words
• share personal words across SpellCheckerService, PROCESS_TEXT and the IME
• refresh an already-running engine when stored words change
• add a dedicated personal dictionary management screen
• keep the activity internal and non-exported
• mark personal dictionary support complete in the roadmap

Engine behavior

• personal words are stored locally
• duplicate additions are ignored
• removed words immediately become invalid again
• personal dictionary changes clear Grammalecte morphology caches
• entries use a neutral morphology tag rather than inventing grammatical information
• dictionary size and entry length are bounded

Validation

• make check
• make assemble
• git diff --check
• real QuickJS / Graphspell smoke tests
• add/remove mutation API tests
• Android instrumentation for persistent dictionary refresh
• manifest test verifies the personal dictionary activity is not exported
• tested on Samsung Galaxy S21 / Android 15 over USB
• verified that an added unknown word is accepted by real correction
• final APK still requests no INTERNET permission