refactor: review fixes and code improvements

- Add shared proxy module (bot/utils/proxy.py) to eliminate duplicate SOCKS5 parsing
- Fix AI client: escape HTML before Markdown→HTML conversion, unify timeouts,
  make health check optional and disabled by default, handle 429 retries
- Fix ai.py: correct forwarded message handling (aiogram 3.x forward_origin),
  pass relevant summaries via extra_system_content
- Fix dialogue.py: only respond to Astra's messages, use system context instead
  of prompt injection, answer on the limit message before phase transition
- Fix voice.py: load Whisper model in thread pool, safe WAV path generation
- Improve database.py: composite indexes, Boolean is_active, upsert file_id cache,
  add context cleanup helper
- Update weather.py and yadisk_download.py to use shared proxy connector
- Update yadisk.py: validate URL before cache clear, add download size limit,
  wrap sync file ops in to_thread
- Reuse S3 client via lru_cache
- Update setup_commands with /aiclear and /aiuser
- Update README, Dockerfile (Python 3.11), docker-compose (mount models)
- Pin dependency versions, remove unused httpx[socks]
- Add basic pytest tests for layout converter and voice normalization

config.py

@@ -23,6 +23,11 @@ AI_PHASE2_LIMIT = 20
 AI_COOLDOWN = 3600
 AI_BLOCK_DEFAULT_DURATION = 86400
 
+# Health check periodically calls every free model to test availability.
+# This consumes API tokens; disabled by default.
+AI_HEALTH_CHECK_ENABLED = os.getenv("AI_HEALTH_CHECK_ENABLED", "false").lower() == "true"
+AI_HEALTH_CHECK_INTERVAL = int(os.getenv("AI_HEALTH_CHECK_INTERVAL", "600"))
+
 ACCESS_KEY = os.getenv("ACCESS_KEY", "").strip()
 SECRET_KEY = os.getenv("SECRET_KEY", "").strip()
 BUCKET_NAME = os.getenv("BUCKET_NAME", "").strip()