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/lib/channel-export.ts

@@ -0,0 +1,20 @@
+import type { ChannelResponse } from "@/lib/types";
+
+export function exportChannel(channel: ChannelResponse): void {
+  const payload = {
+    name: channel.name,
+    description: channel.description ?? undefined,
+    timezone: channel.timezone,
+    blocks: channel.schedule_config.blocks,
+    recycle_policy: channel.recycle_policy,
+  };
+  const blob = new Blob([JSON.stringify(payload, null, 2)], {
+    type: "application/json",
+  });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement("a");
+  a.href = url;
+  a.download = `${channel.name.toLowerCase().replace(/\s+/g, "-")}.json`;
+  a.click();
+  URL.revokeObjectURL(url);
+}