Auto-detect and restart daemon on version mismatch (bd-89)

Implements automatic daemon version detection and restart when client
and daemon versions are incompatible. Eliminates need for manual
'bd daemon --stop' after upgrades.

Changes:
- Check daemon version during health check in PersistentPreRun
- Auto-restart mismatched daemon or fall back to direct mode
- Check version when starting daemon, auto-stop old daemon if incompatible
- Robust restart logic: sets working dir, cleans stale sockets, reaps processes
- Uses waitForSocketReadiness helper for reliable startup detection
- Updated AGENTS.md with version management documentation

Closes bd-89

Amp-Thread-ID: https://ampcode.com/threads/T-231a3701-c9c8-49e4-a1b0-e67c94e5c365
Co-authored-by: Amp <amp@ampcode.com>

AGENTS.md

@@ -70,6 +70,12 @@ The single MCP server instance automatically:
 
 **Note:** The daemon **auto-starts automatically** when you run any `bd` command (v0.9.11+). To disable auto-start, set `BEADS_AUTO_START_DAEMON=false`.
 
+**Version Management:** bd automatically handles daemon version mismatches (v0.16.0+):
+- When you upgrade bd, old daemons are automatically detected and restarted
+- Version compatibility is checked on every connection
+- No manual `bd daemon --stop` required after upgrades
+- Works transparently with MCP server and CLI
+
 **Alternative (legacy): Multiple MCP Server Instances**
 If you must use separate MCP servers (not recommended):
 ```json