feat: Phase N power-user surface (terminal, palette, per-item, sort, url-templates)

- Built-in yt-dlp terminal: src/main/terminal.ts streams raw yt-dlp runs
  (binary fixed, gated on customCommandEnabled), new TerminalView + sidebar tab
- Command palette (Ctrl/Cmd+K), portal-free CommandPalette.tsx wired in App
- Per-playlist-item editing: per-row video/audio toggle + All video/All audio
  batch; addPlaylist enqueues via addMany with per-item kind
- Weighted format sorting: DownloadOptions.formatSort -> raw -S (overrides codec)
- URL-regex template auto-matching: CommandTemplate.urlPattern + selectExtraArgs
  matchesUrl, threaded through resolveExtraArgs; field in TemplateManager

typecheck + test (192) + electron-vite build all clean. Roadmap: Phase N COMPLETE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/terminal.ts

@@ -0,0 +1,99 @@
+/**
+ * Built-in yt-dlp terminal (Phase N): runs the bundled yt-dlp with raw, user-typed
+ * arguments and streams stdout/stderr back to the renderer line-by-line.
+ *
+ * SECURITY: the executable is fixed to the managed yt-dlp (never an arbitrary exe),
+ * and the whole feature is gated on Settings.customCommandEnabled — the same consent
+ * flag that guards per-download extra args, because yt-dlp args can run arbitrary
+ * code (`--exec`). The gate is enforced here in main, not just in the renderer UI.
+ */
+import { spawn, execFile, type ChildProcess } from 'child_process'
+import { existsSync } from 'fs'
+import { type WebContents } from 'electron'
+import { getYtdlpPath, getBinDir, getSystem32Path } from './binaries'
+import { getSettings } from './settings'
+import { ensureManagedYtdlp } from './ytdlp'
+import { parseExtraArgs } from './buildArgs'
+import { IpcChannels, type TerminalEvent, type TerminalRunResult } from '@shared/ipc'
+
+const active = new Map<string, ChildProcess>()
+
+function send(wc: WebContents, ev: TerminalEvent): void {
+  if (!wc.isDestroyed()) wc.send(IpcChannels.terminalOutput, ev)
+}
+
+export function runTerminal(wc: WebContents, id: string, argsRaw: string): TerminalRunResult {
+  if (!getSettings().customCommandEnabled) {
+    return {
+      ok: false,
+      error: 'Enable "Run custom commands" in Settings → Custom commands to use the terminal.'
+    }
+  }
+  ensureManagedYtdlp()
+  const ytdlp = getYtdlpPath()
+  if (!existsSync(ytdlp)) {
+    return { ok: false, error: 'yt-dlp.exe is missing and could not be restored.' }
+  }
+  if (active.has(id)) return { ok: false, error: 'A command is already running.' }
+
+  // Always pin ffmpeg so post-processing works; the rest is whatever the user typed.
+  const args = ['--ffmpeg-location', getBinDir(), ...parseExtraArgs(argsRaw)]
+  let child: ChildProcess
+  try {
+    child = spawn(ytdlp, args, { windowsHide: true })
+  } catch (e) {
+    return { ok: false, error: (e as Error).message }
+  }
+  active.set(id, child)
+
+  // Buffer each stream and emit on newline boundaries (flush the remainder on close).
+  const buffers: Record<'stdout' | 'stderr', string> = { stdout: '', stderr: '' }
+  function feed(stream: 'stdout' | 'stderr', chunk: string): void {
+    buffers[stream] += chunk
+    let nl: number
+    while ((nl = buffers[stream].indexOf('\n')) >= 0) {
+      const line = buffers[stream].slice(0, nl).replace(/\r$/, '')
+      buffers[stream] = buffers[stream].slice(nl + 1)
+      send(wc, { type: 'output', id, line, stream })
+    }
+  }
+  child.stdout?.on('data', (c: Buffer) => feed('stdout', c.toString()))
+  child.stderr?.on('data', (c: Buffer) => feed('stderr', c.toString()))
+
+  let settled = false
+  child.on('error', (err) => {
+    if (settled) return
+    settled = true
+    active.delete(id)
+    send(wc, { type: 'error', id, error: err.message })
+  })
+  child.on('close', (code) => {
+    if (settled) return
+    settled = true
+    active.delete(id)
+    // Flush any trailing partial lines that never hit a newline.
+    for (const stream of ['stdout', 'stderr'] as const) {
+      if (buffers[stream]) send(wc, { type: 'output', id, line: buffers[stream], stream })
+    }
+    send(wc, { type: 'done', id, code })
+  })
+
+  return { ok: true }
+}
+
+export function cancelTerminal(id: string): void {
+  const child = active.get(id)
+  if (!child) return
+  const pid = child.pid
+  if (pid != null) {
+    // Tree-kill via System32 taskkill by absolute path (same hardening as download.ts).
+    execFile(
+      getSystem32Path('taskkill.exe'),
+      ['/pid', String(pid), '/T', '/F'],
+      { windowsHide: true },
+      () => {}
+    )
+  } else {
+    child.kill()
+  }
+}