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

bot/utils/proxy.py

@@ -0,0 +1,41 @@
+import logging
+from urllib.parse import urlparse
+
+from aiohttp_socks import ProxyConnector, ProxyType
+
+from config import PROXY_ENABLED, PROXY_URL
+
+logger = logging.getLogger(__name__)
+
+
+def get_proxy_connector() -> ProxyConnector | None:
+    """Create an aiohttp SOCKS5 proxy connector from PROXY_URL if enabled."""
+    if not PROXY_ENABLED or not PROXY_URL:
+        return None
+
+    parsed = urlparse(PROXY_URL)
+
+    if parsed.scheme not in ("socks5", "socks5h"):
+        logger.warning("Unsupported proxy scheme: %s", parsed.scheme)
+        return None
+
+    host = parsed.hostname
+    port = parsed.port
+    if not host or not port:
+        logger.warning("Invalid proxy URL: missing host or port")
+        return None
+
+    username = parsed.username
+    password = parsed.password
+
+    try:
+        return ProxyConnector(
+            proxy_type=ProxyType.SOCKS5,
+            host=host,
+            port=port,
+            username=username,
+            password=password,
+        )
+    except Exception as exc:
+        logger.error("Failed to create proxy connector: %s", exc)
+        return None