feat: Initialize Electron application with core backend, frontend chat/login UI, and IPC for crypto and link previews.

Frontend/Electron/preload.cjs

@@ -4,6 +4,8 @@ contextBridge.exposeInMainWorld('cryptoAPI', {
     generateKeys: () => ipcRenderer.invoke('generate-keys'),
     randomBytes: (size) => ipcRenderer.invoke('random-bytes', size),
     sha256: (data) => ipcRenderer.invoke('sha256', data),
+    signMessage: (privateKey, message) => ipcRenderer.invoke('sign-message', privateKey, message),
+    verifySignature: (publicKey, message, signature) => ipcRenderer.invoke('verify-signature', publicKey, message, signature),
     deriveAuthKeys: (password, salt) => ipcRenderer.invoke('derive-auth-keys', password, salt),
     encryptData: (data, key) => ipcRenderer.invoke('encrypt-data', data, key),
     decryptData: (encryptedData, key, iv, tag) => ipcRenderer.invoke('decrypt-data', encryptedData, key, iv, tag),