Hide transcript spinner during live meetings

[ComputelessComputer]

Share the transcript tab spinner rule between session headers so active listening keeps the transcript tab idle while finalizing and batch transcription still show progress.

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Note

Low Risk
Small UI-only change to when a header spinner displays; no auth, data, or transcription pipeline logic touched.

Overview
Aligns the outer session header with the note editor so the Transcript tab spinner no longer appears while a meeting is in active (live listening) mode.

Introduces shared helper shouldShowTranscriptTabSpinner, which only returns true for finalizing and running_batch. NoteInput uses it for its header prop, and session/index.tsx replaces the broader isTranscribing check (which previously included active) when driving NoteInputHeader in the outer chrome.

Tests cover that active keeps the spinner off and that finalizing / running_batch still show it.

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