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>

commands/daemon.md

@@ -1,9 +1,9 @@
 ---
-description: Run background sync daemon
-argument-hint: [--stop] [--status] [--health]
+description: Manage background sync daemon
+argument-hint: [--start] [--stop] [--status] [--health]
 ---
 
-Run a per-project background daemon that manages database connections and syncs with git.
+Manage the per-project background daemon that handles database connections and syncs with git.
 
 ## Per-Project Daemon (LSP Model)
 
@@ -39,7 +39,7 @@ Each project runs its own daemon at `.beads/bd.sock` for complete database isola
 
 ## Common Operations
 
-- **Start**: `bd daemon` (auto-starts on first `bd` command)
+- **Start**: `bd daemon --start` (or auto-starts on first `bd` command)
 - **Stop**: `bd daemon --stop`
 - **Status**: `bd daemon --status`
 - **Health**: `bd daemon --health` - shows uptime, cache stats, performance metrics