style(rmi-backend): complete lint cleanup — 1175→0 ruff errors

- Fix 71 invalid-syntax files (class-body newline-broken assignments)
- Add from/None chain to 307 B904 raise-without-from sites
- Add B008 ignore to ruff.toml (already in pyproject.toml)
- Noqa F401 on __init__.py re-exports (137 sites)
- Noqa E402 on deferred imports (63 sites)
- Bulk-add stdlib/FastAPI/project imports for F821 (127 sites)
- Replace ×→x, –→-, …→... in docstrings (4093 chars)
- Manual refactor of 5 SIM103/SIM116 patterns

Tests: 791 passed (66 deselected due to pre-existing Redis issues in test_rag.py)
Co-authored-by: opencode <opencode@rugmunch.io>

scripts/retry_paper_ingest.py

@@ -84,7 +84,7 @@ def main():
         total_chunks += success
         metadata[arxiv_id]["ingested"] = True
         metadata[arxiv_id]["chunk_count"] = success
-        print(f"  {arxiv_id}: {success}/{len(chunks)} chunks — {title[:50]}")
+        print(f"  {arxiv_id}: {success}/{len(chunks)} chunks - {title[:50]}")
 
     with open(METADATA_FILE, "w") as f:
         json.dump(metadata, f, indent=2)