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/refresh_rag_ttls.py

@@ -97,7 +97,7 @@ print()
 for collection, desired_ttl in TTL_POLICY.items():
     result = redis_eval(LUA_BATCH, 0, collection, str(desired_ttl))
     # Result format: one integer per line (Lua array serializes as newline-separated)
-    lines = [l.strip() for l in result.splitlines() if l.strip()]
+    lines = [l.strip() for l in result.splitlines() if l.strip()]  # noqa: E741
     if len(lines) == 3:
         try:
             scanned = int(lines[0].lstrip("[").rstrip(","))