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/setup_x402_rotation.py

@@ -14,7 +14,7 @@ import sys
 sys.path.insert(0, "/root/backend")
 os.chdir("/root/backend")
 
-from app.wallet_manager_v2 import get_wallet_manager_v2
+from app.wallet_manager_v2 import get_wallet_manager_v2  # noqa: E402
 
 # Target addresses from fact_store (id=74)
 EVM_RECEIVING = "0x5761E0337a49819A8Cd4D35D76E882255Cb113b9".lower()