refactor: restructure project layout

- Move main process to electron/main/
- Move preload to electron/preload/
- Add shared types in electron/shared/
- Split redis-service into modular redis/ directory
- Flatten renderer to src/ (remove src/renderer/ nesting)
- Update electron.vite.config.ts paths
- Update tsconfig paths
- Output to electron-dist/

electron/main/credential.ts

@@ -0,0 +1,16 @@
+// src/main/credential.ts
+import { safeStorage } from 'electron'
+
+export function encrypt(text: string): string {
+  if (!safeStorage.isEncryptionAvailable()) {
+    return Buffer.from(text).toString('base64')
+  }
+  return safeStorage.encryptString(text).toString('base64')
+}
+
+export function decrypt(encoded: string): string {
+  if (!safeStorage.isEncryptionAvailable()) {
+    return Buffer.from(encoded, 'base64').toString('utf-8')
+  }
+  return safeStorage.decryptString(Buffer.from(encoded, 'base64'))
+}