Fixes #6431

Summary

• order SqliteSessionService.list_sessions() by update_time ASC with stable user_id / id tie-breakers, appended to both the user-scoped and app-wide SELECT queries
• add a regression where a newly created but stale orphan session must sort before older-but-active sessions, and tied update_time values fall back to id

Why

list_sessions() previously executed without an ORDER BY, so consumers using sessions[-1] for the most recently active session could receive an arbitrary row depending on the SQLite query plan (in practice, primary-key/insertion order).

This mirrors the ordering contract settled in #6272 and implemented in #6276 for DatabaseSessionService; #6276's diff doesn't touch the sqlite backend, leaving the two backends inconsistent. Ordering follows update_time (not create_time) because orphan sessions can be newly created while having stale activity — update_time maps to the returned Session.last_update_time. If that contract changes in review, this should follow.

Testing

• RED before fix: uv run --extra test pytest tests/unittests/sessions/test_session_service.py::test_sqlite_session_service_list_sessions_orders_by_update_time_then_id -q

  E     AssertionError: assert ['active_a', ...le', 'orphan'] == ['orphan', 'm...', 'active_b']
  E       At index 0 diff: 'active_a' != 'orphan'
  1 failed, 4 warnings in 2.80s
  

• GREEN after fix: same focused test → 1 passed, 4 warnings in 2.02s
• uv run --extra test pytest tests/unittests/sessions/test_session_service.py -q → 136 passed, 5 warnings
• uv run --extra dev pyink --check src/google/adk/sessions/sqlite_session_service.py tests/unittests/sessions/test_session_service.py → 2 files would be left unchanged
• uv run --extra dev ruff check src/google/adk/sessions/sqlite_session_service.py tests/unittests/sessions/test_session_service.py → All checks passed!
• git diff --check → clean