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>

app/github_rag_feeder.py

@@ -1,5 +1,5 @@
 """
-RAG GitHub Feeder v2 — Declarative, Config-Driven
+RAG GitHub Feeder v2 - Declarative, Config-Driven
 ==================================================
 Add any GitHub repo as a RAG data source with minimal config.
 Auto-clones, extracts markdown/solidity/text, chunks, and ingests.
@@ -29,7 +29,7 @@ BACKEND = "http://localhost:8000"
 INGEST_URL = f"{BACKEND}/api/v1/rag/ingest"
 
 # ═══════════════════════════════════════════════════
-# DECLARATIVE SOURCE CONFIG — add repos here
+# DECLARATIVE SOURCE CONFIG - add repos here
 # ═══════════════════════════════════════════════════
 SOURCES = [
     {