Scope transcript render subscriptions

[ComputelessComputer]

Replace broad transcript render and export table subscriptions with session-scoped row listener data.

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Note

Medium Risk
Touches live transcript UI, export, and render request assembly; incorrect row scoping could miss updates or over-subscribe, but behavior is covered by existing and updated tests.

Overview
Introduces render-request-hooks so live footer, transcript renderer, and export paths share one way to build RenderTranscriptRequest data without subscribing to whole Tinybase tables.

Subscription model: useSessionTranscriptRenderData / useTranscriptRenderData resolve session transcript IDs and participant mapping IDs from indexes, then useSyncExternalStore bumps a revision when addRowListener fires on only the relevant transcripts, mapping_session_participant, and humans rows. Human rows are limited to session participants, speaker-assignment hints on those transcripts, and the current user—not every human in the store.

Call-site cleanup: during-session, export-data, and renderer/data-hooks drop duplicated useTable + buildRenderTranscriptRequestFromStore logic; the live footer builds transcriptIdByWordId from shared transcriptRows. useTranscriptOffset now depends on useTranscriptRowsRevision instead of the full transcripts table.

render-transcript: adds buildRenderTranscriptRequestFromRows and collectAssignedHumanIdsFromTranscriptRows (exported types for rows/humans). Tests cover assigned-human collection; during-session tests mock addRowListener / delListener for the new hook path.

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