feat: improved OCR pipeline session manager with categories, thumbnails, pipeline logging

- Add document_category (10 types) and pipeline_log JSONB columns
- Session list: thumbnails, copyable IDs, category/doc_type badges
- Inline category dropdown, bulk delete, pipeline step logging
- New endpoints: thumbnail, delete-all, pipeline-log, categories
- Cleared all 22 old test sessions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

klausur-service/backend/ocr_pipeline_session_store.py

@@ -66,7 +66,9 @@ async def init_ocr_pipeline_tables():
             ADD COLUMN IF NOT EXISTS clean_png BYTEA,
             ADD COLUMN IF NOT EXISTS handwriting_removal_meta JSONB,
             ADD COLUMN IF NOT EXISTS doc_type VARCHAR(50),
-            ADD COLUMN IF NOT EXISTS doc_type_result JSONB
+            ADD COLUMN IF NOT EXISTS doc_type_result JSONB,
+            ADD COLUMN IF NOT EXISTS document_category VARCHAR(50),
+            ADD COLUMN IF NOT EXISTS pipeline_log JSONB
         """)
 
 
@@ -91,6 +93,7 @@ async def create_session_db(
                       deskew_result, dewarp_result, column_result, row_result,
                       word_result, ground_truth, auto_shear_degrees,
                       doc_type, doc_type_result,
+                      document_category, pipeline_log,
                       created_at, updated_at
         """, uuid.UUID(session_id), name, filename, original_png)
 
@@ -106,6 +109,7 @@ async def get_session_db(session_id: str) -> Optional[Dict[str, Any]]:
                    deskew_result, dewarp_result, column_result, row_result,
                    word_result, ground_truth, auto_shear_degrees,
                    doc_type, doc_type_result,
+                   document_category, pipeline_log,
                    created_at, updated_at
             FROM ocr_pipeline_sessions WHERE id = $1
         """, uuid.UUID(session_id))
@@ -151,9 +155,10 @@ async def update_session_db(session_id: str, **kwargs) -> Optional[Dict[str, Any
         'deskew_result', 'dewarp_result', 'column_result', 'row_result',
         'word_result', 'ground_truth', 'auto_shear_degrees',
         'doc_type', 'doc_type_result',
+        'document_category', 'pipeline_log',
     }
 
-    jsonb_fields = {'deskew_result', 'dewarp_result', 'column_result', 'row_result', 'word_result', 'ground_truth', 'handwriting_removal_meta', 'doc_type_result'}
+    jsonb_fields = {'deskew_result', 'dewarp_result', 'column_result', 'row_result', 'word_result', 'ground_truth', 'handwriting_removal_meta', 'doc_type_result', 'pipeline_log'}
 
     for key, value in kwargs.items():
         if key in allowed_fields:
@@ -180,6 +185,7 @@ async def update_session_db(session_id: str, **kwargs) -> Optional[Dict[str, Any
                       deskew_result, dewarp_result, column_result, row_result,
                       word_result, ground_truth, auto_shear_degrees,
                       doc_type, doc_type_result,
+                      document_category, pipeline_log,
                       created_at, updated_at
         """, *values)
 
@@ -194,6 +200,7 @@ async def list_sessions_db(limit: int = 50) -> List[Dict[str, Any]]:
     async with pool.acquire() as conn:
         rows = await conn.fetch("""
             SELECT id, name, filename, status, current_step,
+                   document_category, doc_type,
                    created_at, updated_at
             FROM ocr_pipeline_sessions
             ORDER BY created_at DESC
@@ -213,6 +220,18 @@ async def delete_session_db(session_id: str) -> bool:
         return result == "DELETE 1"
 
 
+async def delete_all_sessions_db() -> int:
+    """Delete all sessions. Returns number of deleted rows."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        result = await conn.execute("DELETE FROM ocr_pipeline_sessions")
+        # result is e.g. "DELETE 5"
+        try:
+            return int(result.split()[-1])
+        except (ValueError, IndexError):
+            return 0
+
+
 # =============================================================================
 # HELPER
 # =============================================================================
@@ -235,7 +254,7 @@ def _row_to_dict(row: asyncpg.Record) -> Dict[str, Any]:
             result[key] = result[key].isoformat()
 
     # JSONB → parsed (asyncpg returns str for JSONB)
-    for key in ['deskew_result', 'dewarp_result', 'column_result', 'row_result', 'word_result', 'ground_truth', 'doc_type_result']:
+    for key in ['deskew_result', 'dewarp_result', 'column_result', 'row_result', 'word_result', 'ground_truth', 'doc_type_result', 'pipeline_log']:
         if key in result and result[key] is not None:
             if isinstance(result[key], str):
                 result[key] = json.loads(result[key])