fix(security): comprehensive security hardening — TLS, HMAC WS auth, rate limiting, IP leak prevention

CRITICAL fixes:
- Auto-generated self-signed TLS certs (HTTPS/WSS by default)
- Removed session_key from /srp/verify response (was sent in plaintext)
- Replaced with HMAC-SHA256 ws_token for WebSocket authentication

HIGH fixes:
- WebSocket auth now validates ws_token via hmac.compare_digest()
- /clear endpoint requires Bearer admin_token (printed at server start)
- Password no longer required as CLI arg — supports env var + getpass prompt
- Removed user_ip from Message model (no longer broadcast to clients)

MEDIUM fixes:
- Rate limiter on /srp/init and /srp/verify (10 req/min/IP)
- MessageStore capped at 1000 messages (prevents RAM DoS)
- access_log disabled (was leaking request metadata)

LOW fixes:
- Username sanitization against rich markup injection
- Dead code removed from helpers.py

All 79 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd_chat/server/stores.py

@@ -3,11 +3,14 @@ from .models import Message, UserSession
 
 
 class MessageStore:
-    def __init__(self):
+    def __init__(self, max_messages: int = 1000):
         self._messages: list[Message] = []
+        self._max = max_messages
 
     def add(self, message: Message) -> None:
         self._messages.append(message)
+        if len(self._messages) > self._max:
+            self._messages = self._messages[-self._max:]
 
     def get_all(self) -> list[Message]:
         return self._messages.copy()