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/chat-message-structure.ts

@@ -0,0 +1,21 @@
+import type { ResolvedMention } from "./chat-mentions";
+
+export interface ChatMessageStructureInput {
+  slash: { command: string; args: string } | null;
+  mentions: ResolvedMention[];
+  attachmentFileIds: string[];
+}
+
+export function buildChatMessageStructure(input: ChatMessageStructureInput): string {
+  return JSON.stringify({
+    format: "markdown",
+    slashInvocation: input.slash ? { command: input.slash.command, args: input.slash.args } : null,
+    mentions: input.mentions.map((mention) => ({
+      targetType: mention.target.type,
+      targetId: mention.target.id,
+      offsetStart: mention.offsetStart,
+      offsetEnd: mention.offsetEnd,
+    })),
+    attachmentFileIds: input.attachmentFileIds,
+  });
+}