Upload pipeline: staging, MD5 auto-match, IQDB, three-column board

Backend:
- TempUpload model: staged files (pending / visual_match / completed /
  error) with resolution, e621 payload, custom metadata and IQDB data
- Files land in a temp folder and only move into the watched library
  folder once resolved; duplicates resolve immediately without a copy
- Endpoints: stage (multipart), list, retrieve, temp file, IQDB save,
  resolve (link to post or custom metadata), discard/dismiss
- cleanup_temp_uploads command for old staged files
- Replaces the old direct-to-library upload endpoint

Frontend:
- Upload page is now a three-column board (Pending & Unmatched /
  Visual Similarity Detected / Auto-uploaded & Indexed)
- After upload: MD5s are batch-checked against e621 and matches
  auto-complete with full post metadata; remaining files run through
  IQDB and move to the similarity column when candidates exist
- Metadata modal with IQDB candidates, post-ID linking and custom
  tags/rating/notes; discard and dismiss actions
- e621 client gains fetchPostsByMd5 and iqdbSearch helpers

Roadmap updated with the completed upload items.

backend/apps/library/services.py

@@ -226,6 +226,26 @@ def trim_e621_post(post):
     }
 
 
+def sanitize_iqdb_results(results):
+    """Keep a compact, size-bounded copy of IQDB candidates."""
+    cleaned = []
+    for result in results[:10]:
+        if not isinstance(result, dict):
+            continue
+        score = result.get("score")
+        post_id = result.get("post_id")
+        entry = {
+            "post_id": post_id if isinstance(post_id, int) else None,
+            "score": float(score) if isinstance(score, (int, float)) else None,
+            "preview_url": str(result.get("preview_url") or "")[:500] or None,
+            "rating": str(result.get("rating") or "")[:1] or None,
+            "md5": str(result.get("md5") or "")[:32] or None,
+        }
+        if entry["post_id"] or entry["preview_url"]:
+            cleaned.append(entry)
+    return cleaned
+
+
 def generate_video_thumbnail(md5, path):
     """Extract a JPEG thumbnail from a video, cached under MEDIA_ROOT/thumbs."""
     if not shutil.which("ffmpeg"):