fix: multiple improvements and CI/CD updates

Frontend fixes:
- Add missing translations for chunk upload (upload.uploadingChunks, common.chunk)
- Fix photo deletion visual bug by tracking deletion state per photo
- Prevent UI confusion when deleting photos in admin grid

Backend fixes:
- Add file existence checks before deleting thumbnails
- Prevent ENOENT errors for missing thumbnail files
- Improve error handling in photo deletion

CI/CD updates:
- Remove Gitea release creation from Drone pipeline
- Simplify GitHub mirror workflow (remove history rewriting, keep file removal)
- Add clean-git-history.sh script for manual history cleanup

These changes improve the admin photo management experience and streamline
the CI/CD process for better maintainability.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

frontend/src/i18n/locales/de.json

@@ -35,7 +35,8 @@
     "days": "Tage",
     "customize": "Anpassen",
     "hide": "Ausblenden",
-    "unknown": "Unbekannt"
+    "unknown": "Unbekannt",
+    "chunk": "Teil"
   },
   "upload": {
     "photoCategory": "Fotokategorie",
@@ -51,7 +52,8 @@
     "uploadPhotos": "Fotos hochladen",
     "maxFilesReached": "Maximal 500 Dateien erlaubt",
     "someFilesSkipped": "Einige Dateien wurden übersprungen (500 Dateien Limit)",
-    "tooManyFiles": "Maximal 500 Dateien können gleichzeitig hochgeladen werden"
+    "tooManyFiles": "Maximal 500 Dateien können gleichzeitig hochgeladen werden",
+    "uploadingChunks": "Lade {{count}} Dateien in {{total}} Teilen hoch..."
   },
   "navigation": {
     "dashboard": "Dashboard",

frontend/src/i18n/locales/en.json

@@ -35,7 +35,8 @@
     "days": "days",
     "customize": "Customize",
     "hide": "Hide",
-    "unknown": "Unknown"
+    "unknown": "Unknown",
+    "chunk": "Chunk"
   },
   "upload": {
     "photoCategory": "Photo Category",
@@ -51,7 +52,8 @@
     "uploadPhotos": "Upload Photos",
     "maxFilesReached": "Maximum 500 files allowed",
     "someFilesSkipped": "Some files were skipped (500 file limit)",
-    "tooManyFiles": "Maximum 500 files can be uploaded at once"
+    "tooManyFiles": "Maximum 500 files can be uploaded at once",
+    "uploadingChunks": "Uploading {{count}} files in {{total}} batches..."
   },
   "navigation": {
     "dashboard": "Dashboard",