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/autoflush.go

@@ -671,7 +671,7 @@ func flushToJSONLWithState(state flushState) {
 	issues := make([]*types.Issue, 0, len(issueMap))
 	wispsSkipped := 0
 	for _, issue := range issueMap {
-		if issue.Wisp {
+		if issue.Ephemeral {
 			wispsSkipped++
 			continue
 		}