feat(logging): instrument db operations and transport wrap/unwrap outcomes

[Catrya]

Remaining gaps in the core-flow debug trace (follow-up to #241, closed by
PR #279 :

• db: log migrations as they run, the active backend (SQLite vs
  IndexedDB) at init, and write failures — same levels and redaction
  policy as the existing instrumentation.
• transport: one outcome line per NIP-44 wrap/unwrap (kind, truncated
  event id, ok/error) — decrypt failures are currently near-silent. Never
  the plaintext.

Out of scope: Dart-log unification (tracked in #129) and the chat publish
path (deferred to the chat rework).