refactor: remove unused bd pin/unpin/hook commands (bd-x0zl)

Analysis found these commands are dead code:
- gt never calls `bd pin` - uses `bd update --status=pinned` instead
- Beads.Pin() wrapper exists but is never called
- bd hook functionality duplicated by gt mol status
- Code comment says "pinned field is cosmetic for bd hook visibility"

Removed:
- cmd/bd/pin.go
- cmd/bd/unpin.go
- cmd/bd/hook.go

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor/fix/sync_branch.go

@@ -32,8 +32,7 @@ func SyncBranchConfig(path string) error {
 	}
 
 	// Set sync.branch using bd config set
-	// #nosec G204 - bdBinary is controlled by getBdBinary() which returns os.Executable()
-	setCmd := exec.Command(bdBinary, "config", "set", "sync.branch", currentBranch)
+	setCmd := newBdCmd(bdBinary, "config", "set", "sync.branch", currentBranch)
 	setCmd.Dir = path
 	if output, err := setCmd.CombinedOutput(); err != nil {
 		return fmt.Errorf("failed to set sync.branch: %w\nOutput: %s", err, string(output))