feat(pdfa): add PDF/A archival conversion using ocrmypdf

- Add ENABLE_PDFA_CONVERSION, PDFA_FORMAT, PDFA_UPLOAD_TO_PROVIDERS config settings
- Add original_pdfa_path and processed_pdfa_path columns to FileRecord model
- Create Alembic migration 011_add_pdfa_paths
- Create app/tasks/convert_to_pdfa.py Celery task using ocrmypdf + Ghostscript
- Integrate PDF/A conversion into finalize_document_storage pipeline
- Add comprehensive unit tests (15 tests)
- Update .env.demo and docs/ConfigurationGuide.md

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

app/config.py

@@ -222,6 +222,33 @@ class Settings(BaseSettings):
 
     # Feature flags
     allow_file_delete: bool = True  # Default to allowing file deletion from database
+
+    # PDF/A archival conversion settings
+    enable_pdfa_conversion: bool = Field(
+        default=False,
+        description=(
+            "Enable PDF/A archival variant generation. When enabled, PDF/A copies of both the "
+            "original ingested file and the processed file are created and saved alongside the "
+            "standard copies. Uses ocrmypdf with Ghostscript for the conversion. "
+            "This may double or triple storage but provides better legal coverage. Default: False."
+        ),
+    )
+    pdfa_format: str = Field(
+        default="2",
+        description=(
+            "PDF/A format variant to produce. Passed to ocrmypdf --output-type pdfa-N. "
+            "Valid values: '1' (PDF/A-1b), '2' (PDF/A-2b), '3' (PDF/A-3b). Default: '2'."
+        ),
+    )
+    pdfa_upload_to_providers: bool = Field(
+        default=False,
+        description=(
+            "When enabled and PDF/A conversion is active, also upload the PDF/A variants "
+            "to all configured storage providers in addition to the standard processed file. "
+            "PDF/A files are uploaded with a '-PDFA' suffix in their filename. Default: False."
+        ),
+    )
+
     imap_readonly_mode: bool = Field(
         default=False,
         description=(