Update code references and tests: Bookmann → Bookhoard

Code changes:
- main.go: Update cache directory path
- sidecar.go: Update file extension (.bookmann.json → .bookhoard.json)
- security.go: Update CORS example URLs
- queue_test.go: Update test database name
- feed_test.go: Update test assertions
- phase1_integration_test.go: Update test email addresses
- TEST_COVERAGE.md: Update project references

Part of project rename to Bookhoard.

internal/opds/feed_test.go

@@ -121,7 +121,7 @@ func TestEntrySetIdentifier(t *testing.T) {
 	}
 
 	if entry.Identifier.ID != "bookhoard" {
-		t.Errorf("expected Identifier ID to be 'bookmann', got '%s'", entry.Identifier.ID)
+		t.Errorf("expected Identifier ID to be 'bookhoard', got '%s'", entry.Identifier.ID)
 	}
 
 	if entry.Identifier.Content != "book-uuid-123" {
@@ -139,7 +139,7 @@ func TestEntryAddMetadata(t *testing.T) {
 
 	meta := entry.Metadata[0]
 	if meta.Property != "bookhoard:sha256" {
-		t.Errorf("expected Property to be 'bookmann:sha256', got '%s'", meta.Property)
+		t.Errorf("expected Property to be 'bookhoard:sha256', got '%s'", meta.Property)
 	}
 
 	if meta.Content != "abc123..." {