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/gateway/hooks-mapping.ts

@@ -25,7 +25,8 @@ export type HookMappingResolved = {
     | "discord"
     | "slack"
     | "signal"
-    | "imessage";
+    | "imessage"
+    | "msteams";
   to?: string;
   model?: string;
   thinking?: string;
@@ -65,7 +66,8 @@ export type HookAction =
         | "discord"
         | "slack"
         | "signal"
-        | "imessage";
+        | "imessage"
+        | "msteams";
       to?: string;
       model?: string;
       thinking?: string;