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.

cmd/server/main.go

@@ -98,7 +98,7 @@ func main() {
 	queueHandler := handlers.NewQueueHandler(queries, queueProcessor)
 
 	// Create conversion service for EPUB→KEPUB conversion
-	conversionService := services.NewConversionService(queries, "/var/bookmann/cache/kepub")
+	conversionService := services.NewConversionService(queries, "/var/bookhoard/cache/kepub")
 	opdsHandler := handlers.NewOPDSHandler(queries, conversionService)
 
 	e := echo.New()