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/export_mtime_test.go

@@ -61,6 +61,14 @@ func TestExportUpdatesDatabaseMtime(t *testing.T) {
 		t.Fatalf("Export failed: %v", err)
 	}
 
+	// Update metadata after export (bd-ymj fix)
+	mockLogger := daemonLogger{
+		logFunc: func(format string, args ...interface{}) {
+			t.Logf(format, args...)
+		},
+	}
+	updateExportMetadata(ctx, store, jsonlPath, mockLogger, "")
+
 	// Get JSONL mtime
 	jsonlInfo, err := os.Stat(jsonlPath)
 	if err != nil {
@@ -158,6 +166,14 @@ func TestDaemonExportScenario(t *testing.T) {
 		t.Fatalf("Daemon export failed: %v", err)
 	}
 
+	// Daemon updates metadata after export (bd-ymj fix)
+	mockLogger := daemonLogger{
+		logFunc: func(format string, args ...interface{}) {
+			t.Logf(format, args...)
+		},
+	}
+	updateExportMetadata(ctx, store, jsonlPath, mockLogger, "")
+
 	// THIS IS THE FIX: daemon now calls TouchDatabaseFile after export
 	if err := TouchDatabaseFile(dbPath, jsonlPath); err != nil {
 		t.Fatalf("TouchDatabaseFile failed: %v", err)
@@ -229,6 +245,14 @@ func TestMultipleExportCycles(t *testing.T) {
 			t.Fatalf("Cycle %d: Export failed: %v", i, err)
 		}
 
+		// Update metadata after export (bd-ymj fix)
+		mockLogger := daemonLogger{
+			logFunc: func(format string, args ...interface{}) {
+				t.Logf(format, args...)
+			},
+		}
+		updateExportMetadata(ctx, store, jsonlPath, mockLogger, "")
+
 		// Apply fix
 		if err := TouchDatabaseFile(dbPath, jsonlPath); err != nil {
 			t.Fatalf("Cycle %d: TouchDatabaseFile failed: %v", i, err)