Add Nostr Feed Manager: Rust backend with Electron + React GUI

- Rust library (nostr-manager-backend) with CLI and JSON-lines IPC serve mode:
  profiles, publishing with per-relay reports, relays, settings, vault storage
  and legacy-vault migration
- Electron + React + TypeScript desktop GUI using the same backend over stdio IPC
- Vitest suite with a fake backend speaking the real protocol
- electron-builder linux packaging; README with build and usage instructions

frontend/eslint.config.js

@@ -0,0 +1,19 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+import reactHooks from 'eslint-plugin-react-hooks';
+
+export default tseslint.config(
+  { ignores: ['dist/**', 'dist-electron/**', 'release/**', 'node_modules/**'] },
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    files: ['src/**/*.{ts,tsx}', 'electron/**/*.ts'],
+    plugins: {
+      'react-hooks': reactHooks,
+    },
+    rules: {
+      ...reactHooks.configs.recommended.rules,
+      '@typescript-eslint/no-explicit-any': 'off',
+    },
+  },
+);