CL-6557: Chat: false "no reply arrived" notice after a fully rendered reply

[TheGreatAxios]

Summary

• The reply-timeout backstop in packages/chat-ui/src/streaming-reply.ts fires even after a complete reply has rendered, because it only ever moves a turn to "replied" on the chat.agent stream's connector.reply event — a signal a parked folded run's stream may never carry, and which can otherwise be dropped/delayed independent of the actual reply.
• The reply a reader sees actually arrives as its own chat.message event (posted by postReply in chat-orchestrator.ts), an entirely separate pipeline from chat.agent. When connector.reply never lands but the chat.message does, the client's streamingReply state stays stuck in "awaiting" and the 120s backstop eventually shows the false notice right under the already-rendered reply.
• Fix: an awaiting turn's own chat.message (agent sender, real content, not postUndeliveredNotice's turnFailed part) now also moves the turn to "replied", independent of whether connector.reply ever arrives. The transition is keyed on rendered content — an observable fact — rather than a lifecycle event that may never arrive.
• This is the third instance of this bug family (CL-6432: turn-phase typing indicator (reopened) #183, CL-6486: time out a reply that stalls mid-stream #220); both prior fixes tuned when the backstop arms rather than what disarms it.

Test plan

• packages/chat-ui/src/streaming-reply.test.ts — new pure-reducer cases for the chat.message-driven "replied" transition (agent sender + content → replied; turnFailed notice never counts; human sender never counts; empty parts never count)
• packages/chat-ui/test/use-streaming-reply.test.tsx — hook-level repro: a rendered reply followed by silence with no terminal run event (mimicking a parked folded run) shows no notice; a rendered reply followed by a post-reply tool round shows no notice; a turn with no content at all still times out correctly
• bun test in packages/chat-ui: 661 pass, 0 fail
• tsc --noEmit and eslint clean on changed files
• prettier --check clean on changed files

Linear: CL-6557