Reduce recording start editor renders

[ComputelessComputer]

Keep expensive recording-start hooks out of inactive render branches and read audio existence through a narrow query hook instead of the full playback context.

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This is part 1 of 2 in a stack made with GitButler:

•  2  Reduce session note render cost #5903
•  1  Reduce recording start editor renders #5902 👈

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Note

Low Risk
Mostly UI performance refactors with equivalent behavior; session tab and timeline selection logic are moderately touched but not security- or data-critical paths.

Overview
Cuts unnecessary React work when starting or viewing sessions by narrowing subscriptions and splitting render branches.

Session note tab: useAudioExists reads the same React Query cache as the player but without subscribing to WaveSurfer/playback context. Auto-start listening runs in a small AutoStartListening child instead of the main tab body. TabContentNoteInner builds editor tabs and the active view from explicit state (createEditorTabs, computeCurrentNoteTab, transcript/insights flags) instead of useEditorTabs / useCurrentNoteTab, which pulled in heavier hooks via the audio player context.

Listen FAB: While a session is connecting, only StopListeningButton mounts (stop action); start/configure hooks stay in StartListeningButton when idle.

Sidebar timeline: Timeline items receive a stable getFlatItemKeys() (ref-backed) for shift-range selection instead of a new flatItemKeys array each parent render. ItemBase is memoized with a custom props equality check to limit row re-renders.

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