Promote AgentCompany-New to the repository root and retire the old app

The legacy application - its src, tests, landing site, promo assets, docs,
release tooling, CI workflows, and root configs - leaves the tree; it stays
reachable in history. Everything under AgentCompany-New moves up unchanged:
same package name, so the production userData/database path is untouched,
and e2e/build scripts already resolved paths relative to the project. The
developer cred.txt stays gitignored at its new location. Full verify:ci
passes from the new root.

src/main/services/secret-vault.ts

@@ -0,0 +1,17 @@
+import { safeStorage } from "electron";
+
+export class SecretVault {
+  encryptSecret(secret: string): Buffer {
+    if (!safeStorage.isEncryptionAvailable()) {
+      throw new Error("OS credential encryption is unavailable.");
+    }
+    return safeStorage.encryptString(secret);
+  }
+
+  decryptSecret(ciphertext: Buffer): string {
+    if (!safeStorage.isEncryptionAvailable()) {
+      throw new Error("OS credential encryption is unavailable.");
+    }
+    return safeStorage.decryptString(ciphertext);
+  }
+}