perf(rpc): use bd daemon protocol to reduce subprocess overhead

Replace bd subprocess calls in gt commands with daemon RPC when available.
Each subprocess call has ~40ms overhead for Go binary startup, so using
the daemon's Unix socket protocol significantly reduces latency.

Changes:
- Add RPC client to beads package (beads_rpc.go)
- Modify List/Show/Update/Close methods to try RPC first, fall back to subprocess
- Replace runBdPrime() with direct content output (avoids bd subprocess)
- Replace checkPendingEscalations() to use beads.List() with RPC
- Replace hook.go bd subprocess calls with beads package methods

The RPC client:
- Connects to daemon via Unix socket at .beads/bd.sock
- Uses JSON-based request/response protocol (same as bd daemon)
- Falls back gracefully to subprocess if daemon unavailable
- Lazy-initializes connection on first use

Performance improvement targets (from bd-2zd.2):
- gt prime < 100ms (was 5.8s with subprocess chain)
- gt hook < 100ms (was ~323ms)

Closes: bd-2zd.2

internal/cmd/hook.go

@@ -10,7 +10,6 @@ import (
 	"github.com/spf13/cobra"
 	"github.com/steveyegge/gastown/internal/beads"
 	"github.com/steveyegge/gastown/internal/events"
-	"github.com/steveyegge/gastown/internal/runtime"
 	"github.com/steveyegge/gastown/internal/style"
 )
 
@@ -183,15 +182,8 @@ func runHook(_ *cobra.Command, args []string) error {
 			fmt.Printf("%s Replacing completed bead %s...\n", style.Dim.Render("ℹ"), existing.ID)
 			if !hookDryRun {
 				if hasAttachment {
-					// Close completed molecule bead (use bd close --force for pinned)
-					closeArgs := []string{"close", existing.ID, "--force",
-						"--reason=Auto-replaced by gt hook (molecule complete)"}
-					if sessionID := runtime.SessionIDFromEnv(); sessionID != "" {
-						closeArgs = append(closeArgs, "--session="+sessionID)
-					}
-					closeCmd := exec.Command("bd", closeArgs...)
-					closeCmd.Stderr = os.Stderr
-					if err := closeCmd.Run(); err != nil {
+					// Close completed molecule bead (use force for pinned)
+					if err := b.CloseForced(existing.ID, "Auto-replaced by gt hook (molecule complete)"); err != nil {
 						return fmt.Errorf("closing completed bead %s: %w", existing.ID, err)
 					}
 				} else {
@@ -232,10 +224,9 @@ func runHook(_ *cobra.Command, args []string) error {
 		return nil
 	}
 
-	// Hook the bead using bd update (discovery-based approach)
-	hookCmd := exec.Command("bd", "update", beadID, "--status=hooked", "--assignee="+agentID)
-	hookCmd.Stderr = os.Stderr
-	if err := hookCmd.Run(); err != nil {
+	// Hook the bead using beads package (uses RPC when daemon available)
+	status := beads.StatusHooked
+	if err := b.Update(beadID, beads.UpdateOptions{Status: &status, Assignee: &agentID}); err != nil {
 		return fmt.Errorf("hooking bead: %w", err)
 	}