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/handlers/sidecar.go

@@ -187,7 +187,7 @@ func (h *SidecarHandler) GetSidecarConfig(c echo.Context) error {
 	return c.JSON(http.StatusOK, config)
 }
 
-// DownloadSidecarConfig generates a .bookmann.json file for device setup
+// DownloadSidecarConfig generates a .bookhoard.json file for device setup
 // GET /api/devices/:device_id/sidecar/download
 func (h *SidecarHandler) DownloadSidecarConfig(c echo.Context) error {
 	deviceID, err := uuid.Parse(c.Param("device_id"))
@@ -324,7 +324,7 @@ func (h *SidecarHandler) DownloadSidecarConfig(c echo.Context) error {
 	}
 
 	// Set headers for file download
-	filename := fmt.Sprintf("%s.bookmann.json", sanitizeFilename(device.DeviceName))
+	filename := fmt.Sprintf("%s.bookhoard.json", sanitizeFilename(device.DeviceName))
 	c.Response().Header().Set("Content-Type", "application/json")
 	c.Response().Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))