feat(desktop): port v0.11.4-v0.15.2 from Tauri to Electron + Discord-parity audio (v0.16.0)

Chronological port of every Tauri release commit (v0.11.4 -> v0.15.2)
into the Electron rebuild, plus Discord-style audio handling that goes
beyond the Tauri original.

Highlights:
  - All 17 Tauri release commits ported (audio fixes, custom notification
    sound, Discord-style chat UX, profile banner, changelog page,
    Discord-parity call UX, screen-share echo + re-watch UX, audio-loop
    fix).
  - Native napi-rs audio-loopback addon with WASAPI process-loopback:
      * EXCLUDE_TARGET_PROCESS_TREE for full-screen shares -> peers
        never hear themselves echoed back through the capture.
      * INCLUDE_TARGET_PROCESS_TREE for window shares -> only the
        picked window's audio is captured, not the whole OS mixer
        (Discord parity).
      * HWND -> PID resolution via Win32 GetWindowThreadProcessId.
  - Discord-style screen-source picker (thumbnail grid, screens vs
    apps tabs, live-refreshing thumbnails).
  - Hash routing fix for packaged builds (file:// can't resolve
    BrowserRouter paths).
  - Tauri sources removed (apps/desktop/src-tauri).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/electron/modules/fs-scoped.ts

@@ -0,0 +1,81 @@
+// Scoped filesystem. Every renderer-supplied path is resolved under
+// `app.getPath('userData')`. Post-normalisation we re-check the resolved
+// absolute path is still contained in the root; anything that breaks out
+// (via .., symlink, absolute path) is rejected. Binary payloads are
+// base64 on the wire because JSON IPC can't carry raw bytes cleanly.
+
+import { app, ipcMain } from 'electron';
+import { promises as fs } from 'node:fs';
+import path from 'node:path';
+
+import { CHANNELS, type FsPath, type FsRenameArgs, type FsWriteArgs } from '../ipc-types';
+
+function rootDir(): string {
+  return app.getPath('userData');
+}
+
+function resolveScoped(rel: FsPath): string {
+  const root = rootDir();
+  if (path.isAbsolute(rel)) {
+    throw new Error('fs-scoped: absolute path rejected');
+  }
+  const normalised = path.normalize(rel);
+  if (normalised.split(/[\\/]/).includes('..')) {
+    throw new Error('fs-scoped: path traversal rejected');
+  }
+  const abs = path.resolve(root, normalised);
+  const withSep = root.endsWith(path.sep) ? root : root + path.sep;
+  if (abs !== root && !abs.startsWith(withSep)) {
+    throw new Error('fs-scoped: escaped scope');
+  }
+  return abs;
+}
+
+export function register(): void {
+  ipcMain.handle(CHANNELS.FS_APP_LOCAL_DATA_DIR, async (): Promise<string> => rootDir());
+
+  ipcMain.handle(CHANNELS.FS_READ, async (_evt, rel: FsPath): Promise<string | null> => {
+    const abs = resolveScoped(rel);
+    try {
+      const buf = await fs.readFile(abs);
+      return buf.toString('base64');
+    } catch (err: unknown) {
+      if ((err as NodeJS.ErrnoException).code === 'ENOENT') return null;
+      throw err;
+    }
+  });
+
+  ipcMain.handle(CHANNELS.FS_WRITE, async (_evt, args: FsWriteArgs): Promise<void> => {
+    const abs = resolveScoped(args.path);
+    await fs.mkdir(path.dirname(abs), { recursive: true });
+    const buf = Buffer.from(args.dataBase64, 'base64');
+    await fs.writeFile(abs, buf);
+  });
+
+  ipcMain.handle(CHANNELS.FS_EXISTS, async (_evt, rel: FsPath): Promise<boolean> => {
+    const abs = resolveScoped(rel);
+    try {
+      await fs.access(abs);
+      return true;
+    } catch {
+      return false;
+    }
+  });
+
+  ipcMain.handle(CHANNELS.FS_MKDIR, async (_evt, rel: FsPath): Promise<void> => {
+    const abs = resolveScoped(rel);
+    await fs.mkdir(abs, { recursive: true });
+  });
+
+  ipcMain.handle(CHANNELS.FS_RENAME, async (_evt, args: FsRenameArgs): Promise<void> => {
+    const from = resolveScoped(args.from);
+    const to = resolveScoped(args.to);
+    await fs.mkdir(path.dirname(to), { recursive: true });
+    await fs.rename(from, to);
+  });
+
+  ipcMain.handle(CHANNELS.FS_REMOVE, async (_evt, rel: FsPath): Promise<void> => {
+    const abs = resolveScoped(rel);
+    await fs.rm(abs, { recursive: true, force: true });
+  });
+}