Fix websocket chat history ordering

[pmbstyle]

What changed

• order list_memory_entries_by_chat() by created_at DESC, rowid DESC instead of id DESC
• add a regression test that proves UUID order can differ from message chronology

Why

Desktop WebSocket reconnect history now reads recent messages from stored memory entries. The SQLite query was sorting by random uuid4 IDs, so reconnects could show an arbitrary slice of history instead of the latest turns.

Impact

• desktop chat history on reconnect now uses actual message time ordering
• the regression is covered at the store layer where the bug originates

Validation

• python3 -m py_compile src/octopal/infrastructure/store/sqlite.py tests/test_memory_system.py
• git diff --check
• uv run pytest tests/test_memory_system.py tests/test_gateway_ws_resolution.py -q could not complete in this environment because uv hit DNS/download failures fetching fsspec==2026.1.0