Name the background effect pieces after background effects

- One name, as review asked: TrackProcessorContext becomes
  BackgroundEffectsContext, with BackgroundEffectsProvider,
  BackgroundEffectsState, useBackgroundEffects,
  useBackgroundEffectsState$ and useSyncBackgroundEffects.
- The state's Behavior is backgroundEffectsState$ wherever it is passed,
  in place of trackProcessorState$, trackerProcessorState$ and
  processorState$.
- Renames only: nothing changes in behaviour.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

component/index.tsx

@@ -74,7 +74,7 @@ import {
 import { MediaDevicesContext } from "../src/MediaDevicesContext";
 import { MediaDevices } from "../src/state/MediaDevices";
 import { ObservableScope } from "../src/state/ObservableScope";
-import { ProcessorProvider } from "../src/livekit/TrackProcessorContext";
+import { BackgroundEffectsProvider } from "../src/livekit/BackgroundEffectsContext";
 import { Config } from "../src/config/Config";
 import { type ConfigOptions } from "../src/config/ConfigOptions";
 import { i18n } from "../src/utils/i18n";
@@ -252,7 +252,7 @@ export const ElementCall: FC<ElementCallProps> = ({
                       <TooltipProvider>
                         <ClientProvider client={client}>
                           <MediaDevicesContext value={mediaDevices}>
-                            <ProcessorProvider>
+                            <BackgroundEffectsProvider>
                               <CallView
                                 client={client}
                                 rtcSession={rtcSession}
@@ -261,7 +261,7 @@ export const ElementCall: FC<ElementCallProps> = ({
                                 preload={params.preload}
                                 skipLobby={params.skipLobby}
                               />
-                            </ProcessorProvider>
+                            </BackgroundEffectsProvider>
                           </MediaDevicesContext>
                         </ClientProvider>
                       </TooltipProvider>