feat: add bd doctor check for orphaned issues (bd-5hrq)

- Add CheckOrphanedIssues to detect issues referenced in commits but still open
- Pattern matches (prefix-xxx) in git log against open issues in database
- Reports warning with issue IDs and commit hashes
- Add 8 comprehensive tests for the new check

Also:
- Add tests for mol spawn --attach functionality (bd-f7p1)
- Document commit message convention in AGENT_INSTRUCTIONS.md
- Fix CheckpointWAL to use wrapDBError for consistency

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

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

AGENT_INSTRUCTIONS.md

@@ -61,6 +61,17 @@ func TestMyFeature(t *testing.T) {
 3. **Update docs**: If you changed behavior, update README.md or other docs
 4. **Commit**: Issues auto-sync to `.beads/issues.jsonl` and import after pull
 
+### Commit Message Convention
+
+When committing work for an issue, include the issue ID in parentheses at the end:
+
+```bash
+git commit -m "Fix auth validation bug (bd-abc)"
+git commit -m "Add retry logic for database locks (bd-xyz)"
+```
+
+This enables `bd doctor` to detect **orphaned issues** - work that was committed but the issue wasn't closed. The doctor check cross-references open issues against git history to find these orphans.
+
 ### Git Workflow
 
 **Auto-sync provides batching!** bd automatically: