feat: Add --start flag to bd daemon, show help with no args

Currently 'bd daemon' with no args immediately starts the daemon. This is
inconsistent with other daemon management commands like --stop, --status,
etc. and makes the command less discoverable for new users.

Changes:
- Add --start flag to explicitly start daemon
- Show help text when no operation flags provided
- Update auto-start logic to use --start flag
- Update startDaemon() to pass --start when forking
- Update all documentation to use 'bd daemon --start'
- Update MCP Python client error messages

The MCP docs already incorrectly showed 'bd daemon start' which doesn't
work, so this change fixes that documentation bug while improving UX.

Auto-start still works correctly - it now passes --start internally.

Fixes bd-gfu

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

integrations/beads-mcp/src/beads_mcp/bd_daemon_client.py

@@ -110,7 +110,7 @@ class BdDaemonClient(BdClientBase):
         
         # No socket found anywhere
         raise DaemonNotRunningError(
-            "Daemon socket not found. Is the daemon running? Try: bd daemon (local) or bd daemon --global"
+            "Daemon socket not found. Is the daemon running? Try: bd daemon --start"
         )
 
     async def _send_request(self, operation: str, args: Dict[str, Any]) -> Any: