feat(pdfa): add FreeTSA timestamping, per-provider folder overrides, individual upload toggles

- Add RFC 3161 timestamping via FreeTSA (PDFA_TIMESTAMP_ENABLED, PDFA_TIMESTAMP_URL)
- Replace PDFA_UPLOAD_TO_PROVIDERS with individual PDFA_UPLOAD_ORIGINAL and PDFA_UPLOAD_PROCESSED
- Add PDFA_UPLOAD_FOLDER setting for per-provider subfolder configuration
- Add GOOGLE_DRIVE_PDFA_FOLDER_ID for Google Drive-specific folder override
- Add folder_override parameter to all 8 folder-using upload tasks
- Add folder_overrides dict parameter to send_to_all_destinations
- Add _compute_pdfa_folder_overrides() and _timestamp_file() helpers
- Expand tests to 26 (timestamping, folder overrides, individual toggles)
- Update docs/ConfigurationGuide.md and .env.demo

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/tasks/upload_to_google_drive.py

@@ -153,7 +153,9 @@ def truncate_property_value(key, value, max_bytes=100):
 
 
 @celery.task(base=UploadTaskWithRetry, bind=True)
-def upload_to_google_drive(self, file_path: str, include_metadata=True, file_id: int = None):
+def upload_to_google_drive(
+    self, file_path: str, include_metadata=True, file_id: int = None, folder_override: str = None
+):
     """
     Uploads a file to Google Drive in the configured folder with optional metadata.
 
@@ -201,8 +203,9 @@ def upload_to_google_drive(self, file_path: str, include_metadata=True, file_id:
         }
 
         # If folder ID is specified, set parent folder
-        if settings.google_drive_folder_id:
-            file_metadata["parents"] = [settings.google_drive_folder_id]
+        gdrive_folder_id = folder_override if folder_override is not None else settings.google_drive_folder_id
+        if gdrive_folder_id:
+            file_metadata["parents"] = [gdrive_folder_id]
 
         # Add custom properties if metadata exists
         if metadata: