fix(security): resolve Snyk/bandit code analysis findings

- config.py: move REPORT_OUTPUT_DIR from /tmp (world-writable) to /app/reports
  to prevent CWE-377 symlink attack vector (B108, only real security issue)
- main.py: log startup seed failures instead of silently swallowing them (B110)
- Add # nosec annotations to intentional try/except patterns that are by design:
  Jira integration errors, email failures, DetachedInstanceError, storage errors,
  and Jira session timeout (all B110/B112 false positives)
- Add # nosec B105 to false positives where bandit misidentifies config key
  names and masking strings as hardcoded passwords
- Add .bandit config to skip B311 in seed_demo.py (random used for fake
  demo data generation, not cryptographic purposes)

backend/app/routers/admin_config.py

@@ -149,7 +149,7 @@ def export_config(
             "email": u.email if hasattr(u, "email") else None,
             "role": u.role,
             "is_active": u.is_active,
-            "must_change_password": True,  # force password reset on new instance
+            "must_change_password": True,  # force password reset on new instance  # nosec B105
         }
         for u in db.query(User).order_by(User.username).all()
     ]