feat(anime): add anime browser powered by Aniyomi extensions

- Add `subminer anime` / `--anime` and a tray entry to open a browser that searches installed Aniyomi extension sources, shows cover art and episodes, and plays into mpv with overlay/mining attached
- Add an Extensions tab to add repos and install/update/remove sources, and per-source settings for sources needing config
- Support searching all sources at once with streaming, per-source results and status
- Prefer Japanese audio/subtitle tracks from the source and keep the primary subtitle slot reserved for Japanese
- Fix window/tray/Dock handling so the browser and mpv can be switched between without quitting the app or losing the Dock icon
- Add anime.repos, anime.extensionsDir, anime.preferredQuality config keys (no bundled repos or discovery)

src/anime-bridge/extension-installer.ts

@@ -0,0 +1,66 @@
+import { mkdir, rm, writeFile } from 'node:fs/promises';
+import path from 'node:path';
+import { extensionFileName, type RepoExtension } from './extension-repo';
+
+/**
+ * Downloads extension APKs into the extensions directory.
+ *
+ * Only URLs that came from a repository index the user configured are ever
+ * fetched; nothing here discovers or suggests sources.
+ */
+
+export interface InstallExtensionOptions {
+  extensionsDir: string;
+  extension: RepoExtension;
+  fetchImpl?: typeof fetch;
+  /** Guards against a mistyped repo serving something enormous. */
+  maxBytes?: number;
+}
+
+/** APKs are a few MB; anything far past that is not an extension. */
+const DEFAULT_MAX_BYTES = 64 * 1024 * 1024;
+
+const APK_MAGIC = [0x50, 0x4b, 0x03, 0x04]; // "PK\x03\x04" — APKs are zip archives.
+
+export function looksLikeApk(bytes: Uint8Array): boolean {
+  return APK_MAGIC.every((byte, index) => bytes[index] === byte);
+}
+
+/**
+ * Download one extension into `extensionsDir`, replacing any previous version.
+ *
+ * The file is named after the package so an update overwrites in place rather
+ * than leaving two versions for the bridge to load.
+ */
+export async function installExtension(options: InstallExtensionOptions): Promise<string> {
+  const fetchImpl = options.fetchImpl ?? fetch;
+  const maxBytes = options.maxBytes ?? DEFAULT_MAX_BYTES;
+
+  const response = await fetchImpl(options.extension.apkUrl);
+  if (!response.ok) {
+    throw new Error(`Downloading ${options.extension.name} failed (${response.status}).`);
+  }
+
+  const declared = Number(response.headers.get('content-length') ?? '0');
+  if (declared > maxBytes) {
+    throw new Error(`${options.extension.name} is larger than the ${maxBytes} byte limit.`);
+  }
+
+  const bytes = new Uint8Array(await response.arrayBuffer());
+  if (bytes.byteLength > maxBytes) {
+    throw new Error(`${options.extension.name} is larger than the ${maxBytes} byte limit.`);
+  }
+  if (!looksLikeApk(bytes)) {
+    throw new Error(`${options.extension.name} did not download as an APK.`);
+  }
+
+  await mkdir(options.extensionsDir, { recursive: true });
+  const target = path.join(options.extensionsDir, extensionFileName(options.extension.pkg));
+  await writeFile(target, bytes);
+  return target;
+}
+
+/** Delete an installed extension. Missing files are treated as already gone. */
+export async function removeExtension(extensionsDir: string, pkg: string): Promise<void> {
+  await rm(path.join(extensionsDir, extensionFileName(pkg)), { force: true });
+}