Export and display close reasons for issues (beads-410)

- Add CloseReason field to Issue struct in types.go
- Add GetCloseReason() and batch GetCloseReasonsForIssues()
- Update issue loading to populate close reasons
- Update scanIssues() to include close_reason in JSONL export
- Update bd show to display close reason after status

Close reasons now survive sync between repos.

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

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

cmd/bd/sync.go

@@ -332,7 +332,12 @@ Use --merge to merge the sync branch back to main branch.`,
 						if err != nil {
 							fmt.Fprintf(os.Stderr, "Warning: failed to count issues after import: %v\n", err)
 						} else {
-							if err := validatePostImport(beforeCount, afterCount, jsonlPath); err != nil {
+							// Account for expected deletions from sanitize step (bd-tt0 fix)
+							expectedDeletions := 0
+							if sanitizeResult != nil {
+								expectedDeletions = sanitizeResult.RemovedCount
+							}
+							if err := validatePostImportWithExpectedDeletions(beforeCount, afterCount, expectedDeletions, jsonlPath); err != nil {
 								fmt.Fprintf(os.Stderr, "Post-import validation failed: %v\n", err)
 								os.Exit(1)
 							}