feat(msteams): add MS Teams provider skeleton

- Add Microsoft 365 Agents SDK packages (@microsoft/agents-hosting,
  @microsoft/agents-hosting-express, @microsoft/agents-hosting-extensions-teams)
- Add MSTeamsConfig type and zod schema
- Create src/msteams/ provider with monitor, token, send, probe
- Wire provider into gateway (server-providers.ts, server.ts)
- Add msteams to all provider type unions (hooks, queue, cron, etc.)
- Update implementation guide with new SDK and progress

src/msteams/token.ts

@@ -0,0 +1,23 @@
+import type { MSTeamsConfig } from "../config/types.js";
+
+export type MSTeamsCredentials = {
+  appId: string;
+  appPassword: string;
+  tenantId: string;
+};
+
+export function resolveMSTeamsCredentials(
+  cfg?: MSTeamsConfig,
+): MSTeamsCredentials | undefined {
+  const appId = cfg?.appId?.trim() || process.env.MSTEAMS_APP_ID?.trim();
+  const appPassword =
+    cfg?.appPassword?.trim() || process.env.MSTEAMS_APP_PASSWORD?.trim();
+  const tenantId =
+    cfg?.tenantId?.trim() || process.env.MSTEAMS_TENANT_ID?.trim();
+
+  if (!appId || !appPassword || !tenantId) {
+    return undefined;
+  }
+
+  return { appId, appPassword, tenantId };
+}