refactor(frontend): extract logic to hooks, split inline components

Area 1 (tv/page.tsx 964→423 lines):
- hooks: use-fullscreen, use-idle, use-volume, use-quality, use-subtitles,
  use-channel-input, use-channel-passwords, use-tv-keyboard
- components: SubtitlePicker, VolumeControl, QualityPicker, TopControlBar,
  LogoWatermark, AutoplayPrompt, ChannelNumberOverlay, TvBaseLayer

Area 2 (edit-channel-sheet.tsx 1244→678 lines):
- hooks: use-channel-form (all form state + reset logic)
- lib/schemas.ts: extracted Zod schemas + extractErrors
- components: AlgorithmicFilterEditor, RecyclePolicyEditor, WebhookEditor,
  AccessSettingsEditor, LogoEditor

Area 3 (dashboard/page.tsx 406→261 lines):
- hooks: use-channel-order, use-import-channel, use-regenerate-all
- lib/channel-export.ts: pure export utility
- components: DashboardHeader

k-tv-frontend/hooks/use-volume.ts

@@ -0,0 +1,39 @@
+"use client";
+
+import { useState, useEffect, useCallback, useRef, RefObject } from "react";
+import { Volume1, Volume2, VolumeX } from "lucide-react";
+
+export function useVolume(
+  videoRef: RefObject<HTMLVideoElement | null>,
+  isCasting: boolean,
+) {
+  const [volume, setVolume] = useState(1);
+  const [isMuted, setIsMuted] = useState(false);
+  const [showSlider, setShowSlider] = useState(false);
+
+  // Sync to video element
+  useEffect(() => {
+    if (!videoRef.current) return;
+    videoRef.current.muted = isMuted;
+    videoRef.current.volume = volume;
+  }, [isMuted, volume, videoRef]);
+
+  // Auto-mute when casting, restore on cast end
+  const prevMutedRef = useRef(false);
+  useEffect(() => {
+    if (isCasting) {
+      prevMutedRef.current = isMuted;
+      setIsMuted(true);
+    } else {
+      setIsMuted(prevMutedRef.current);
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [isCasting]);
+
+  const toggleMute = useCallback(() => setIsMuted((m) => !m), []);
+
+  const VolumeIcon =
+    isMuted || volume === 0 ? VolumeX : volume < 0.5 ? Volume1 : Volume2;
+
+  return { volume, setVolume, isMuted, setIsMuted, toggleMute, VolumeIcon, showSlider, setShowSlider };
+}