feat: add hbc_mini single-file client; drop dead connections on protocol error

- scripts/hbc_mini.py: self-contained hbc with no external deps; uses
  /proc for CPU/memory/network on Linux, df for disk, JSON config
- hbc + hbc_mini: mark connection _dead and stop sending on protocol error
- README: document hbc_mini usage, config, and plugin availability
- pyproject.toml: include hbc_mini.py in script-files

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

hbd/client/main.py

@@ -55,7 +55,8 @@ class AsyncConnection:
         
         self.transport: Optional[asyncio.DatagramTransport] = None
         self.protocol: Optional[asyncio.DatagramProtocol] = None
-        
+        self._dead = False
+
         self.logger = logging.getLogger(f"hbc.conn.{addr}")
     
     async def open(self) -> bool:
@@ -92,9 +93,12 @@ class AsyncConnection:
             msg: Message dictionary
             msg_id: Message ID (HTB, PLG, etc.)
         """
+        if self._dead:
+            return
+
         if not self.transport:
             await self.open()
-        
+
         if not self.transport:
             self.logger.error("Cannot send - no transport")
             return
@@ -166,7 +170,9 @@ class HeartbeatProtocol(asyncio.DatagramProtocol):
     
     def error_received(self, exc):
         """Handle protocol errors."""
-        self.logger.error(f"Protocol error: {exc}")
+        self.logger.warning(f"Protocol error on {self.connection.addr}: {exc} — dropping connection")
+        self.connection._dead = True
+        self.connection.close()
 
 
 async def handle_command(conn: AsyncConnection, msg: dict):