fix: address code review feedback

- Use astimezone() instead of replace() for timezone conversion in is_token_expired
- Log cleanup exceptions with logger.exception() in signup
- Add security warning when STRIPE_WEBHOOK_SECRET is not configured
- Increase Stripe price ID column length from 64 to 128 characters
- Replace alert() with aria-live assertive region in pricing.html
- Convert auth() login tests to use pytest.mark.asyncio and await

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

app/api/local_auth.py

@@ -187,6 +187,7 @@ async def signup(request: Request, body: SignupBody, db: DbSession) -> dict[str,
             db.commit()
         except Exception:
             db.rollback()
+            logger.exception("Failed to clean up orphan records for %s after email send failure", body.email)
         logger.warning("Signup email failed for %s: %s", body.email, exc)
         raise HTTPException(
             status_code=status.HTTP_503_SERVICE_UNAVAILABLE,