fix: add Pin/Unpin methods and call bd pin in pinToHook (gt-o3is)

Adds Pin() and Unpin() methods to the beads wrapper that call bd pin/unpin.

Updates pinToHook() to call b.Pin() after AttachMolecule() to set the
pinned boolean field and assignee on the work issue. This should enable
bd hook to show pinned work.

NOTE: There's a known issue where bd pin via subprocess doesn't actually
set the pinned field even though it reports success. The handoff bead
attachment remains the primary mechanism until this is resolved.

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

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

internal/cmd/sling.go

@@ -1057,11 +1057,21 @@ func pinToHook(beadsPath, agentAddress, issueID string, moleculeCtx *MoleculeCon
 		attachedMolecule = moleculeCtx.RootIssueID
 	}
 
-	// Attach molecule to handoff bead
+	// Attach molecule to handoff bead (stores in description)
 	_, err = b.AttachMolecule(handoff.ID, attachedMolecule)
 	if err != nil {
 		return fmt.Errorf("attaching molecule: %w", err)
 	}
 
+	// Also pin the work issue itself to the agent
+	// This sets the pinned boolean field AND assignee so bd hook can find it
+	// NOTE: There's a known issue (gt-o3is) where bd pin via subprocess doesn't
+	// actually set the pinned field, even though it reports success.
+	if err := b.Pin(attachedMolecule, role); err != nil {
+		// Non-fatal - the handoff bead attachment is the primary mechanism
+		// This just enables bd hook visibility
+		fmt.Printf("  %s pin work issue: %v\n", style.Dim.Render("Note: could not"), err)
+	}
+
 	return nil
 }