[sundruid]

What changed

• tolerate SQLite closure while an event-stream handler performs final IRC
  presence cleanup
• add a regression test that forces this shutdown order
• record the cleanup in the 1.6.1 changelog

Why

The full Raspberry Pi suite passed, but its deliberately temporary database
could be removed just before a daemon event-stream thread performed its final
irc_leave. That produced a harmless background traceback after a successful
test. Production storage is persistent, but shutdown should still be clean.

Validation

• Python compile check
• 41 tests passing locally (2 Linux-only SO_PEERCRED tests skipped on macOS)
• dedicated simulated database-close regression test
• git diff --check