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/oauth/pkce.ts

@@ -0,0 +1,13 @@
+import { createHash, randomBytes } from "node:crypto";
+
+export interface PkcePair {
+  verifier: string;
+  challenge: string;
+}
+
+/** Generate a PKCE verifier and its S256 challenge (RFC 7636). */
+export function generatePkce(): PkcePair {
+  const verifier = randomBytes(32).toString("base64url");
+  const challenge = createHash("sha256").update(verifier).digest("base64url");
+  return { verifier, challenge };
+}