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/tsconfig.electron.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "CommonJS",
+    "moduleResolution": "node",
+    "lib": ["ES2022"],
+    "types": ["node"],
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "outDir": "dist-electron",
+    "rootDir": "electron"
+  },
+  "include": ["electron"]
+}