feat(plugins): add plugin windows, CLI actions, and data dirs

- Add `--plugin-action <id>/<name>` CLI flag, dispatched via runPluginAction
- Add ctx.ui.openWindow for plugin-owned BrowserWindows with sandboxed preload
- Add ctx.dataDir (`plugin-data/<id>/`), ctx.actions.run, ctx.mpv.ensureRunning
- Emit mpv end-file events to plugins with reason, entry id, and error
- Run Windows .cmd/.bat shims through cmd.exe in exec, killing the tree on abort
- Update plugin docs, usage, architecture notes, and e2e coverage

src/core/utils/windows-command-shim.ts

@@ -0,0 +1,83 @@
+import fs from 'node:fs';
+import path from 'node:path';
+
+/** True for batch shims (`.cmd`/`.bat`), which Windows only runs through cmd.exe. */
+export function isWindowsCommandShim(command: string): boolean {
+  return /\.(cmd|bat)$/i.test(command);
+}
+
+/**
+ * Resolves an extensionless Windows command the way cmd.exe does: each `PATHEXT` extension in
+ * the command's own directory, or in each `PATH` entry for a bare name. Returns `command`
+ * unchanged when it already has an extension or nothing matches.
+ */
+export function resolveWindowsCommand(
+  command: string,
+  env: NodeJS.ProcessEnv,
+  existsSync: (candidate: string) => boolean = fs.existsSync,
+): string {
+  if (path.extname(command)) return command;
+  const directory = path.dirname(command);
+  const directories =
+    directory === '.' ? (env.PATH ?? env.Path ?? '').split(path.delimiter).filter(Boolean) : [''];
+  const extensions = (env.PATHEXT ?? '.COM;.EXE;.BAT;.CMD').split(';').filter(Boolean);
+  for (const entry of directories) {
+    for (const extension of extensions) {
+      const candidate = entry ? path.join(entry, command + extension) : command + extension;
+      if (existsSync(candidate)) return candidate;
+    }
+  }
+  return command;
+}
+
+/*!
+ * Windows command escaping adapted from cross-spawn 7.0.6.
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2018 Made With MOXY Lda <hello@moxy.studio>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+const WINDOWS_SHELL_META_CHARACTERS = /([()\][%!^"`<>&|;, *?])/g;
+
+// Quote for both cmd.exe and the Windows argv parser. The outer caret escapes
+// are consumed by cmd, leaving the quoted argument unchanged for the command.
+function escapeWindowsShellArgument(value: string): string {
+  const quotesEscaped = value
+    .replace(/(?=(\\+?)?)\1"/g, '$1$1\\"')
+    .replace(/(?=(\\+?)?)\1$/, '$1$1');
+  return `"${quotesEscaped}"`.replace(WINDOWS_SHELL_META_CHARACTERS, '^$1');
+}
+
+/**
+ * Builds the cmd.exe invocation that runs a batch shim with `args`. Spawn the result with
+ * `windowsVerbatimArguments: true` so Node does not re-quote the prepared command line.
+ */
+export function buildWindowsShimInvocation(
+  command: string,
+  args: readonly string[],
+  env: NodeJS.ProcessEnv,
+): { file: string; args: string[] } {
+  const commandLine = [command, ...args].map(escapeWindowsShellArgument).join(' ');
+  return {
+    file: env.ComSpec ?? env.COMSPEC ?? process.env.ComSpec ?? 'cmd.exe',
+    args: ['/d', '/s', '/v:off', '/c', `"${commandLine}"`],
+  };
+}