revert(31,32): restore pre-optimization state to fix VU/slider perf

Phase 31 selector optimization and Phase 32 state update changes
caused VU meters to animate slowly and volume sliders to be
unresponsive. Reverted all affected files to pre-Phase-31 state.

Files reverted:
- useMixerHelper.js: back to individual selectors (no shallowEqual)
- mixersSlice.js: removed composed selectors
- JKSessionScreen.js: pre-Phase-32 state
- useSessionModel.js: pre-Phase-32 debounce changes

Performance issues resolved:
- VU meter animations now smooth
- Volume sliders respond immediately

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

jam-ui/src/store/features/mixersSlice.js

@@ -1,4 +1,4 @@
-import { createSlice, createSelector } from '@reduxjs/toolkit';
+import { createSlice } from '@reduxjs/toolkit';
 
 const initialState = {
   // Core mixer collections
@@ -313,69 +313,3 @@ export const selectMixerPairByResourceId = (resourceId) => (state) => {
 export const selectMixerPairByTrackId = (trackId) => (state) => {
   return state.mixers.mixersByTrackId[trackId];
 };
-
-// Composed memoized selectors for useMixerHelper optimization
-// These group related data that's typically used together
-
-export const selectCoreMixerState = createSelector(
-  [selectChatMixer, selectBroadcastMixer, selectRecordingMixer],
-  (chatMixer, broadcastMixer, recordingMixer) => ({
-    chatMixer,
-    broadcastMixer,
-    recordingMixer
-  })
-);
-
-export const selectTrackMixerState = createSelector(
-  [
-    selectRecordingTrackMixers,
-    selectBackingTrackMixers,
-    selectJamTrackMixers,
-    selectMetronomeTrackMixers,
-    selectAdhocTrackMixers
-  ],
-  (recordingTrackMixers, backingTrackMixers, jamTrackMixers, metronomeTrackMixers, adhocTrackMixers) => ({
-    recordingTrackMixers,
-    backingTrackMixers,
-    jamTrackMixers,
-    metronomeTrackMixers,
-    adhocTrackMixers
-  })
-);
-
-export const selectMixerLookupTables = createSelector(
-  [selectAllMixers, selectMixersByResourceId, selectMixersByTrackId],
-  (allMixers, mixersByResourceId, mixersByTrackId) => ({
-    allMixers,
-    mixersByResourceId,
-    mixersByTrackId
-  })
-);
-
-export const selectMasterPersonalMixers = createSelector(
-  [selectMasterMixers, selectPersonalMixers],
-  (masterMixers, personalMixers) => ({
-    masterMixers,
-    personalMixers
-  })
-);
-
-export const selectMixerMetadata = createSelector(
-  [selectMetronome, selectMetronomeSettings, selectMediaSummary, selectNoAudioUsers, selectClientsWithAudioOverride, selectMixersReady],
-  (metronome, metronomeSettings, mediaSummary, noAudioUsers, clientsWithAudioOverride, isReady) => ({
-    metronome,
-    metronomeSettings,
-    mediaSummary,
-    noAudioUsers,
-    clientsWithAudioOverride,
-    isReady
-  })
-);
-
-export const selectSimulatedCategoryMixers = createSelector(
-  [selectSimulatedMusicCategoryMixers, selectSimulatedChatCategoryMixers],
-  (simulatedMusicCategoryMixers, simulatedChatCategoryMixers) => ({
-    simulatedMusicCategoryMixers,
-    simulatedChatCategoryMixers
-  })
-);