Final cleanup: Update remaining comments and variable names

Changes:
- Update comments: "Bookmann UUID" → "Bookhoard UUID"
- Rename sidecar struct field: Bookmann → Bookhoard
- Update type names: SidecarBookmannConfig → SidecarBookhoardConfig
- Fix test database name in queue_test.go
- Fix uppercase env var examples in KOBO_SETUP.md

Internal Go variable names (BookmannUuid, bookmannUUID) left unchanged
as they're implementation details that don't affect functionality.

Part of project rename to Bookhoard.

internal/services/book_matching.go

@@ -60,7 +60,7 @@ func NewBookMatchingService(db *database.Queries) *BookMatchingService {
 func (s *BookMatchingService) QueryBooks(ctx context.Context, req *BookQueryRequest) (*BookQueryResponse, error) {
 	var matches []BookMatch
 
-	// Priority 1: Bookmann UUID (canonical) - Confidence: 1.0
+	// Priority 1: Bookhoard UUID (canonical) - Confidence: 1.0
 	if match := s.matchByBookhoardUUID(ctx, req.Identifiers); match != nil {
 		matches = append(matches, *match)
 	}
@@ -113,7 +113,7 @@ func (s *BookMatchingService) QueryBooks(ctx context.Context, req *BookQueryRequ
 	}, nil
 }
 
-// matchByBookhoardUUID attempts to match by Bookmann UUID
+// matchByBookhoardUUID attempts to match by Bookhoard UUID
 func (s *BookMatchingService) matchByBookhoardUUID(ctx context.Context, identifiers []string) *BookMatch {
 	for _, id := range identifiers {
 		if len(id) > 4 && id[:4] == "uuid:" {