refactor(backend): migrate to tauri v2 sidecars and resolve pipe deadlocks

- Replace tokio::process with tauri_plugin_shell sidecar API for native cross-compilation bundle execution.
- Implement non-blocking stdout/stderr multiplexing in yt-dlp spawn to prevent OS pipe buffer deadlocks.
- Refactor capabilities to restrict execution explicitly to sidecars instead of wildcards.
- Rename local binaries to strictly adhere to target-triple architecture suffixes.
- Drop manual get_binary_name path resolutions in favor of Tauri's externalBin bundler.

scripts/verify-binaries.js

@@ -0,0 +1,57 @@
+const fs = require('fs');
+const path = require('path');
+const os = require('os');
+
+// Maps Node's os.arch() to Rust's target_arch
+const archMap = {
+  'x64': 'x86_64',
+  'arm64': 'aarch64'
+};
+
+// Maps Node's os.platform() to Rust's target_os/target_env
+const platformMap = {
+  'darwin': 'apple-darwin',
+  'win32': 'pc-windows-msvc',
+  'linux': 'unknown-linux-gnu'
+};
+
+const currentArch = archMap[os.arch()];
+const currentPlatform = platformMap[os.platform()];
+
+if (!currentArch || !currentPlatform) {
+  console.error(`Unsupported architecture or platform: ${os.arch()} / ${os.platform()}`);
+  process.exit(1);
+}
+
+const targetTriple = `${currentArch}-${currentPlatform}`;
+const isWindows = os.platform() === 'win32';
+const ext = isWindows ? '.exe' : '';
+const suffix = `-${targetTriple}${ext}`;
+
+const binariesDir = path.join(__dirname, '..', 'src-tauri', 'binaries');
+const requiredBinaries = ['yt-dlp', 'aria2c', 'ffmpeg', 'deno'];
+
+console.log(`Verifying target sidecars for: ${targetTriple}`);
+
+let missing = false;
+
+for (const bin of requiredBinaries) {
+  const expectedName = `${bin}${suffix}`;
+  const binPath = path.join(binariesDir, expectedName);
+
+  if (!fs.existsSync(binPath)) {
+    console.error(`[ERROR] Missing strictly required sidecar: ${expectedName} in src-tauri/binaries/`);
+    missing = true;
+  } else {
+    console.log(`[OK] Found sidecar: ${expectedName}`);
+  }
+}
+
+if (missing) {
+  console.error('\nPlease download or build the missing target triple binaries and place them in the src-tauri/binaries directory.');
+  console.error('Build blocked due to missing architecture-aware sidecars.');
+  process.exit(1);
+}
+
+console.log('All required sidecars are present.');
+process.exit(0);