Make Buzz conversation status and indicators durable

[RossHartmann]

Summary

• Project durable agent status as channel-window auxiliary data so it remains visible below a root even when the thread is closed and has no reply/unread metadata.
• Preserve the in-thread projection, coalesce by signed actor/channel/root/receipt, suppress nonterminal status after same-agent final evidence, and retain terminal errors.
• Make message indicators authoritative and state-driven: queued eyes, running/retrying speech, terminal warning, and final/cancel cleanup, with per-message sequencing that prevents stale asynchronous writes.

Companion plan and cross-repo delivery

Companion Buzz plan

Authoritative Mono plan and recovery PR: Kiingo/kiingo#12383.

Verified locally

• Focused desktop status/window tests: 42/42.
• Desktop typecheck and scoped Biome.
• Relay final-evidence suppression regression: 1/1.
• ACP mapping, publication reassertion, generation sequencing, panic/error warning, and final cleanup tests.
• Workspace Rust fmt.
• buzz-acp and buzz-relay clippy with warnings denied.
• Branch based on current origin/main before push.

Delivery checklist

• Relevant required CI is green.
• Mono recovery PR is merged.
• Production deployment is green.
• Bounded live status/indicator verification is green.