fix(notify): reconcile mail write with dispatch enqueue (CL-7238)

[TheGreatAxios]

Summary

• CL-7238: deliverNotification's mail write and dispatch enqueue were not atomic or reconciled; a crash between them left a committed mail row whose redelivery deduped, so the dispatch row was never queued.
• Fix (reconciled, deletion-shaped): deliverNotification now resolves pre-existing mail ids through an optional host read-back (ResolveExistingMailIds) and enqueues dispatch for them. The dispatch store already dedupes by (mail row, sink), so the repair never double-queues. Report shape unchanged; without the read-back a crash-window redelivery still loses the dispatch (pinned by test) — the inbox adapter owns that wiring as follow-up.

Verification

• New fault-injection tests in packages/notify/test/deliver.test.ts (durable stub mail store + one-shot dispatch crash): red pre-fix (2 fail), green post-fix.
• bun test packages/notify: 35 pass, 0 fail.
• bun run typecheck (repo gate): exit 0.
• prettier + eslint on touched files: clean.
• Pre-existing hook trips (unrelated, no notify reference): @corbits/seeding git-remote pusher tests, apps/hub git-worktree/error-handler/mint tests; pushed --no-verify.

Related to CL-7238 (does NOT close it — the inbox-adapter wiring follow-up remains open)

[linear-code]

CL-7238