feat: Multi-guild support implementation

- Added multi-guild support with comma-separated AllowedGuildIDs config
- Per-guild embed tracking with isolated state
- Per-server action locking to prevent race conditions across guilds
- Cross-guild embed updates after power actions
- Debug logging for embed update triggers
- Fixed resource usage field formatting (brackets now properly closed)
- Updated config.ini.sample, generate_config.py for backward compatibility
- Updated README.md with multi-guild documentation
- Updated tests for multi-guild support

models.py

@@ -101,11 +101,17 @@ class ServerListResponse(BaseModel):
 
 
 class EmbedLocation(BaseModel):
-    """Embed location tracking data."""
+    """Embed location tracking data with guild context."""
 
+    guild_id: int
     channel_id: str
     message_id: str
 
+    # Composite key for storage
+    @property
+    def storage_key(self) -> str:
+        return f"{self.guild_id}:{self.channel_id}:{self.message_id}"
+
 
 # Rebuild models to resolve forward references
 ResourceAttributes.model_rebuild()