[chore] Remove stale unused '# ty: ignore[invalid-argument-type]' in db/connection.py

[100yenadmin]

src/lossless_hermes/db/connection.py:~918 carries a # ty: ignore[invalid-argument-type] suppression that ty now reports as unused (the diagnostic it suppressed no longer fires). Flagged independently by 4+ v0.2.0 executor agents. CI's ty check passes (the unused-suppression is warning-level, ty exits 0), so it's not breaking anything — just persistent noise that every agent touching nearby code re-flags.

Fix: remove the stale # ty: ignore[...] directive (one line). Verify ty check src scripts stays clean.

Target: v0.2.0 chore (or fold into any nearby PR).