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-mentions.ts

@@ -0,0 +1,87 @@
+import type { DatabaseSync } from "node:sqlite";
+import { canonicalMentionHandle } from "../../shared/mention-handles";
+
+export interface MentionTarget {
+  type: "employee" | "agent" | "board" | "org_group";
+  id: string;
+}
+
+interface MentionCandidate extends MentionTarget {
+  handle: string;
+}
+
+export interface ResolvedMention {
+  target: MentionTarget;
+  offsetStart: number;
+  offsetEnd: number;
+}
+
+export function resolveChatMentions(db: DatabaseSync, orgId: string, spaceId: string, body: string): ResolvedMention[] {
+  const mentions: ResolvedMention[] = [];
+  const seen = new Set<string>();
+  for (const match of body.matchAll(/(^|\s)@([A-Za-z][A-Za-z0-9_-]{1,63})/g)) {
+    const token = match[2];
+    const target = resolveMention(db, orgId, spaceId, token);
+    const offsetStart = match.index + match[1].length;
+    const key = `${target.type}:${target.id}:${offsetStart}`;
+    if (seen.has(key)) continue;
+    seen.add(key);
+    mentions.push({ target, offsetStart, offsetEnd: offsetStart + token.length + 1 });
+  }
+  return mentions;
+}
+
+export function recordChatMentions(db: DatabaseSync, messageId: string, mentions: ResolvedMention[]): void {
+  for (const mention of mentions) {
+    db.prepare(`
+      insert into chat_mentions(message_id, target_type, target_id, offset_start, offset_end)
+      values (?, ?, ?, ?, ?)
+    `).run(messageId, mention.target.type, mention.target.id, mention.offsetStart, mention.offsetEnd);
+  }
+}
+
+function resolveMention(db: DatabaseSync, orgId: string, spaceId: string, token: string): MentionTarget {
+  const handles = mentionLookupHandles(token);
+  if (handles.has("board")) return { type: "board", id: orgId };
+  if (handles.has("oncall")) return { type: "org_group", id: `${orgId}:oncall` };
+  const candidates = mentionCandidates(db, orgId, spaceId).filter((candidate) => handles.has(candidate.handle));
+  const unique = new Map(candidates.map((candidate) => [`${candidate.type}:${candidate.id}`, candidate]));
+  if (unique.size === 0) throw new Error(`Mention @${token} could not be resolved.`);
+  if (unique.size > 1) throw new Error(`Mention @${token} is ambiguous.`);
+  const target = [...unique.values()][0];
+  return { type: target.type, id: target.id };
+}
+
+function mentionCandidates(db: DatabaseSync, orgId: string, spaceId: string): MentionCandidate[] {
+  const employees = db.prepare(`
+    select employees.id, employees.display_name
+    from employees
+    join chat_memberships memberships
+      on memberships.principal_type = 'employee'
+      and memberships.principal_id = employees.id
+      and memberships.space_id = ?
+    where employees.org_id = ?
+  `).all(spaceId, orgId) as Array<{ id: string; display_name: string }>;
+  const agents = db.prepare(`
+    select agents.id, agents.name
+    from agents
+    join chat_memberships memberships
+      on memberships.principal_type = 'agent'
+      and memberships.principal_id = agents.id
+      and memberships.space_id = ?
+    where agents.org_id = ?
+  `).all(spaceId, orgId) as Array<{ id: string; name: string }>;
+  return [
+    ...employees.flatMap((employee) => principalMentionHandles("employee", employee.id, employee.display_name)),
+    ...agents.flatMap((agent) => principalMentionHandles("agent", agent.id, agent.name)),
+  ];
+}
+
+function principalMentionHandles(type: "employee" | "agent", id: string, name: string): MentionCandidate[] {
+  const handles = new Set([canonicalMentionHandle(name), id.toLowerCase()].filter((handle) => handle.length > 0));
+  return [...handles].map((handle) => ({ type, id, handle }));
+}
+
+function mentionLookupHandles(token: string): Set<string> {
+  return new Set([token.toLowerCase(), canonicalMentionHandle(token)].filter((handle) => handle.length > 0));
+}