Reconcile queued Discord member subscriptions after gateway session resume #42

A reconnect can discard an unsent Discord member subscription while retaining local state that says the subscription was already sent. A successful session resume does not reconcile that state, potentially leaving the member pane pending even though the gateway is connected.

Relevant paths in crates/chatd/src/adapters/discord/:

• members.rs::subscribe assigns Watched.sent when enqueueing the desired subscription, before the gateway actually writes it.
• gateway.rs::run clears the outbox when a new gateway connection is established.
• On RESUMED, ready.rs::resumed restores cached presence but does not requeue/reconcile the current member subscription.
• An unchanged Watch is ignored, and an identical desired subscription is deduplicated against Watched.sent.

A concrete failure sequence is: queue a viewport subscription, lose the connection before sending it, clear the queue on reconnect, then successfully resume. Discord may retain the earlier viewport while chatd considers the discarded newer viewport subscribed. Repeated cache reads do not repair this mismatch.

Observed symptom during member-pane investigation: occasional initial loading skeletons lasting seconds, with immediate Members cache replies containing pending: true, no groups and no rows. Laptop suspend/network loss was also observed. The causal connection between that live symptom and this code path has not yet been reproduced or confirmed. Merely resuming a session with an already-delivered subscription is not evidence of failure.

Expected behavior: after resume, reconcile the latest desired viewport with what was actually delivered. Preserve or regenerate discarded subscription state without treating queued frames as acknowledged subscriptions. Handle obsolete roster data consistently when the viewport changed while offline.

Suggested regression coverage: interrupt the connection with a subscription still queued, resume the existing session, and verify that the latest viewport is delivered and its member cache can fill. Include viewport changes while disconnected.

Related: #40 introduces viewport-driven member caching and coalesced subscription snapshots. This issue tracks reconnect recovery separately; #40 explicitly does not claim to resolve intermittent initial loading.