fix(relay): log event kind on accepted /events bridge requests

[subashmokshya]

What

The relay's HTTP bridge terminal attribution line for an accepted event logs accepted but not kind:

{"pubkey":"d5b0ab11…","route":"/events","status":200,"accepted":true,"...":"HTTP bridge request"}

Typing indicators (kind 7) and their deletions (kind 5) travel the same /events route as real messages (kind 9), so every agent turn produces accepted:true lines whether or not a message was actually sent — a silent no-op is indistinguishable from a real send without querying Postgres directly. This has misled at least two separate debugging sessions (see #4676).

Change

kind_u32 is already computed in submit_event_authed before ingest. This PR threads it through the SubmitOutcome::Ok variant and adds it to the info! attribution line. The Rejected arm already logs kind; this closes the gap on the accepted arm.

Now an accepted message vs. an accepted typing indicator are distinguishable at a glance:

route:"/events" status:200 accepted:true kind:9   ← real message
route:"/events" status:200 accepted:true kind:7   ← typing indicator

Scope kept intentionally minimal (kind only). The issue also mentions channel_id as a "nice to have"; happy to add it in a follow-up if wanted — it needs the h tag extracted before the event is moved into ingest_event, so it's a slightly larger change than this one-field fix.

Verification

• cargo check -p buzz-relay — clean
• cargo clippy -p buzz-relay -- -D warnings — clean
• cargo fmt --check — clean

Testing note

The existing attribution tests (submit_event_invalid_json_…, submit_event_relay_only_kind_…) cover the ParseFail and Rejected arms and remain green — this change doesn't touch them. There is no dedicated Ok/accepted-arm attribution test; adding one requires a member pubkey + valid channel event against a live Postgres (the #[ignore = "requires Postgres"] tier). I'm glad to add a T3c asserting the accepted line carries kind= if you'd like it in this PR.

Fixes #4676

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Developed with AI assistance (Claude Code); reviewed and verified locally by me.