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/create_form.go

@@ -111,6 +111,7 @@ func CreateIssueFromFormValues(ctx context.Context, s storage.Storage, fv *creat
 		IssueType:          types.IssueType(fv.IssueType),
 		Assignee:           fv.Assignee,
 		ExternalRef:        externalRefPtr,
+		CreatedBy:          getActorWithGit(), // GH#748: track who created the issue
 	}
 
 	// Check if any dependencies are discovered-from type