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/package.json

@@ -0,0 +1,73 @@
+{
+  "name": "nost-feed-manager",
+  "productName": "Nostr Feed Manager",
+  "version": "0.1.0",
+  "description": "A friendly Linux desktop app for managing Nostr profiles and publishing text notes.",
+  "private": true,
+  "main": "dist-electron/main.js",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc --noEmit -p tsconfig.json && vite build",
+    "typecheck": "tsc --noEmit -p tsconfig.json",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "lint": "eslint src electron eslint.config.js",
+    "lint:fix": "eslint src electron eslint.config.js --fix",
+    "format": "prettier --write .",
+    "format:check": "prettier --check .",
+    "electron:build": "tsc -p tsconfig.electron.json",
+    "start": "npm run electron:build && electron .",
+    "dist": "npm run build && npm run electron:build && electron-builder --linux dir"
+  },
+  "dependencies": {
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1"
+  },
+  "devDependencies": {
+    "@eslint/js": "^9.15.0",
+    "@testing-library/dom": "^10.4.0",
+    "@testing-library/jest-dom": "^6.6.3",
+    "@testing-library/react": "^16.1.0",
+    "@testing-library/user-event": "^14.5.2",
+    "@types/node": "^26.1.2",
+    "@types/react": "^18.3.12",
+    "@types/react-dom": "^18.3.1",
+    "@vitejs/plugin-react": "^4.3.4",
+    "electron": "^33.2.0",
+    "electron-builder": "^25.1.8",
+    "eslint": "^9.15.0",
+    "eslint-plugin-react-hooks": "^5.0.0",
+    "jsdom": "^25.0.1",
+    "prettier": "^3.3.3",
+    "typescript": "^5.6.3",
+    "typescript-eslint": "^8.15.0",
+    "vite": "^5.4.11",
+    "vitest": "^2.1.8"
+  },
+  "build": {
+    "appId": "dev.nostfeedmanager.desktop",
+    "productName": "Nostr Feed Manager",
+    "directories": {
+      "output": "release",
+      "buildResources": "build"
+    },
+    "files": [
+      "dist/**",
+      "dist-electron/**",
+      "package.json"
+    ],
+    "extraResources": [
+      {
+        "from": "../target/release/nostr-manager-backend",
+        "to": "nostr-manager-backend"
+      }
+    ],
+    "linux": {
+      "target": [
+        "dir"
+      ],
+      "category": "Network",
+      "executableName": "nost-feed-manager"
+    }
+  }
+}