docs: mark each key's default in llm.example.toml; gitignore llm.toml

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

.gitignore

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