feat(auth): migrate JWT from HS256 to RS256

- Add services/auth/app/config.py with JWT_PRIVATE_KEY and JWT_PUBLIC_KEY
  (Auth Service local config - private key never leaves this service)
- Update routes.py: sign tokens with RS256 private key
- Update deps.py + verify.py: verify tokens with RS256 public key
- Update shared/config.py: replace JWT_SECRET/JWT_ALGORITHM with
  JWT_PUBLIC_KEY (for optional local verification by other services)
- Add sys.path fix in main.py for local dev without PYTHONPATH

services/auth/app/main.py

@@ -4,7 +4,16 @@ Standalone FastAPI service extracted from the adiuva-api monolith.
 Owns: users, refresh_tokens, subscriptions (read).
 """
 
+import sys
 from contextlib import asynccontextmanager
+from pathlib import Path
+
+# Ensure the repo root is on sys.path so "shared" is importable.
+# In Docker, COPY shared/ puts it at /app/shared/ (already importable).
+# In local dev, we need to add the repo root (two levels up from this file).
+_repo_root = str(Path(__file__).resolve().parents[3])
+if _repo_root not in sys.path:
+    sys.path.insert(0, _repo_root)
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware