Add user-configurable TTS pronunciation overrides

A JSON map (TTS_PRONUNCIATIONS_PATH, default tts_pronunciations.json)
rewrites mispronounced words — place names, initialisms, dotted
abbreviations — to phonetic spellings before synthesis, applied after
markdown cleanup in both /tts/speech paths. Whole-word smartcase
matching (lowercase keys match any casing, uppercase keys exact),
longest key wins, hot-reloaded on mtime change with last-good fallback
on parse errors. See tts_pronunciations.example.json.

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

.gitignore

@@ -5,6 +5,8 @@ database/target
 *.db-shm
 *.db-wal
 .env
+# Server-local TTS pronunciation overrides (tts_pronunciations.example.json is the template)
+/tts_pronunciations.json
 /tmp
 /docs
 /specs