feat(31-01): add composed memoized selectors to mixersSlice

- Add createSelector import from @reduxjs/toolkit
- Add selectCoreMixerState (chatMixer, broadcastMixer, recordingMixer)
- Add selectTrackMixerState (5 track mixer arrays)
- Add selectMixerLookupTables (allMixers, mixersByResourceId, mixersByTrackId)
- Add selectMasterPersonalMixers (masterMixers, personalMixers)
- Add selectMixerMetadata (metronome, settings, mediaSummary, noAudioUsers, etc)
- Add selectSimulatedCategoryMixers (simulatedMusic, simulatedChat)

These composed selectors memoize grouped state objects, reducing
selector overhead from 18+ individual subscriptions to 6 memoized selectors.

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

@@ -1,4 +1,4 @@
-import { createSlice } from '@reduxjs/toolkit';
+import { createSlice, createSelector } from '@reduxjs/toolkit';
 
 const initialState = {
   // Core mixer collections
@@ -313,3 +313,69 @@ 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
+  })
+);