feat(mcp): agent save_page_version tool — collab stateless transport + role prompts (#370)

Stage A of #370: wire the MCP client transport for the already-shipped server
save-version handler (PR-1 #374). An agent can now pin an intentional named
version (kind='agent', derived server-side from the signed actor) of a page's
CURRENT live collaboration content.

- collab-session.ts: add CollabSession.sendStatelessAndAwait(payload, predicate,
  timeoutMs) — sends a stateless message over the live provider and resolves on
  the first matching reply, with a bounded timeout; lifecycle (inflightReject,
  ready-guard, concurrent fail-fast, idle re-arm) mirrors mutate(). Extend
  CollabProviderLike with sendStateless + the stateless on/off overloads.
- collaboration.ts: add savePageVersionRealtime() — under withPageLock, reuse the
  cached agent-authenticated CollabSession (#400), send {type:'save-version'},
  await {type:'version.saved', …}; no REST read (would race the stale page row).
- client/pages.ts: add savePageVersion(pageId) — resolvePageId +
  getCollabTokenWithReauth + writeWithCollabAuthRetry (#486 self-heal).
- tool-specs.ts: add the deferred savePageVersion spec (+ DocmostClientLike Pick);
  auto-registered on both hosts by the shared loops.
- server-instructions.ts: HISTORY family + routing-prose mention.
- ai-chat-tools.service.ts: contract type-assert for the new client method.
- agent-roles-catalog: tell the content-authoring roles (researcher,
  call-summarizer, ru+en) to save a version when the document is done; bump
  their catalog versions.
- test: unit coverage for savePageVersionRealtime (ack + bounded-timeout paths).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts

@@ -106,6 +106,7 @@ function __assertClientCallContract(client: DocmostClientLike): void {
   void client.sharePage(s, true);
   void client.unsharePage(s);
   void client.restorePageVersion(s);
+  void client.savePageVersion(s);
   void client.transformPage(s, s, { dryRun: true });
   void client.stashPage(s);
   // --- write (image / footnote), in-app since #410 ---