Order live transcription posts by timestamp

[Gokias]

Motivation

• Live transcription lines were being posted in the order chunks finished transcribing, which caused out-of-order display when chunks complete late or concurrently.
• Buffering structured utterances and emitting them by timestamp with a small watermark gives deterministic ordering while still keeping latency low.

Description

• Replaced the plain-string live buffer with a structured buffer pending_live_entries: list[dict] and added pending_live_lock to coordinate access to it.
• build_transcript_lines_for_chunk now includes chunk_id with each entry and returns structured entries { "absolute_start", "chunk_id", "line" }.
• transcription_worker_loop enqueues structured entries into session.pending_live_entries under the lock instead of posting immediately when a chunk finishes.
• transcription_live_loop applies a small watermark (emit_cutoff = now - session.started_at - TRANSCRIBE_EMIT_INTERVAL_SECONDS), extracts ready entries, sorts them by (absolute_start, chunk_id), and then posts them in order.
• try_post_live_lines signature was updated to accept structured entries and sends only entry["line"], re-buffering structured entries on failure.
• The existing final transcript generation remains unchanged and still sorts all lines by absolute_start.

Testing

• Ran python -m py_compile poopbot.py to validate syntax and it completed successfully.

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Codex Task