Remove dead channel/mention code — DM-only bot cleanup

MeshAI is now DM-only. Removed all unreachable channel response
paths, @mention detection, ChannelsConfig, and channel TUI menu.
Fixed restart mechanism with integrated watcher and SIGKILL fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

meshai/config.py

@@ -17,7 +17,6 @@ class BotConfig:
 
     name: str = "ai"
     owner: str = ""
-    respond_to_mentions: bool = True
     respond_to_dms: bool = True
     filter_bbs_protocols: bool = True
 
@@ -32,14 +31,6 @@ class ConnectionConfig:
     tcp_port: int = 4403
 
 
-@dataclass
-class ChannelsConfig:
-    """Channel filtering settings."""
-
-    mode: str = "all"  # all or whitelist
-    whitelist: list[int] = field(default_factory=lambda: [0])
-
-
 @dataclass
 class ResponseConfig:
     """Response behavior settings."""
@@ -134,7 +125,6 @@ class Config:
 
     bot: BotConfig = field(default_factory=BotConfig)
     connection: ConnectionConfig = field(default_factory=ConnectionConfig)
-    channels: ChannelsConfig = field(default_factory=ChannelsConfig)
     response: ResponseConfig = field(default_factory=ResponseConfig)
     history: HistoryConfig = field(default_factory=HistoryConfig)
     memory: MemoryConfig = field(default_factory=MemoryConfig)