Fix bd-ar2 code review issues: metadata tracking and multi-repo support

This commit addresses critical code review findings from bd-dvd and bd-ymj fixes:

## Completed Tasks

### bd-ar2.1: Extract duplicated metadata update code
- Created `updateExportMetadata()` helper function
- Eliminated 22-line duplication between createExportFunc and createSyncFunc
- Single source of truth for metadata updates

### bd-ar2.2: Add multi-repo support to export metadata updates
- Added per-repo metadata key tracking with keySuffix parameter
- Both export and sync functions now update metadata for all repos

### bd-ar2.3: Fix tests to use actual daemon functions
- TestExportUpdatesMetadata now calls updateExportMetadata() directly
- Added TestUpdateExportMetadataMultiRepo() for multi-repo testing
- Fixed export_mtime_test.go tests to call updateExportMetadata()

### bd-ar2.9: Fix variable shadowing in GetNextChildID
- Changed `err` to `resurrectErr` to avoid shadowing
- Improves code clarity and passes linter checks

### bd-ar2.10: Fix hasJSONLChanged to support per-repo keys
- Updated hasJSONLChanged() to accept keySuffix parameter
- Reads metadata with correct per-repo keys
- All callers updated (validatePreExport, daemon import, sync command)

### bd-ar2.11: Use stable repo identifiers instead of paths
- Added getRepoKeyForPath() helper function
- Uses stable identifiers like ".", "../frontend" instead of absolute paths
- Metadata keys now portable across machines and clones
- Prevents orphaned metadata when repos are moved

## Files Changed
- cmd/bd/daemon_sync.go: Helper functions, metadata updates
- cmd/bd/integrity.go: hasJSONLChanged() with keySuffix support
- cmd/bd/sync.go: Updated to use getRepoKeyForPath()
- cmd/bd/*_test.go: Tests updated for new signatures
- internal/storage/sqlite/hash_ids.go: Fixed variable shadowing

## Testing
All export, sync, and integrity tests pass.

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

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

cmd/bd/sync.go

@@ -129,7 +129,9 @@ Use --merge to merge the sync branch back to main branch.`,
 			// Smart conflict resolution: if JSONL content changed, auto-import first
 			// Use content-based check (not mtime) to avoid git resurrection bug (bd-khnb)
 			if err := ensureStoreActive(); err == nil && store != nil {
-				if hasJSONLChanged(ctx, store, jsonlPath) {
+				// Use getRepoKeyForPath for multi-repo support (bd-ar2.10, bd-ar2.11)
+			repoKey := getRepoKeyForPath(jsonlPath)
+			if hasJSONLChanged(ctx, store, jsonlPath, repoKey) {
 					fmt.Println("→ JSONL content changed, importing first...")
 					if err := importFromJSONL(ctx, jsonlPath, renameOnImport); err != nil {
 						fmt.Fprintf(os.Stderr, "Error auto-importing: %v\n", err)