docs(page-templates): document that lookupTemplate is flat (no server recursion) (#54)

Assessment of the page-embed depth/cycle cap: the server /pages/template/lookup
returns FLAT single-level content and does NOT recurse into embedded pages — the
recursive expansion + the PAGE_EMBED_MAX_DEPTH cap are entirely client render
concerns, and a scripted client is already bounded by the per-user throttle
(30/min) + the ArrayMaxSize(50) per-call cap. So no server-side depth guard is
needed; documented at lookupTemplate so future readers don't add a redundant one
or assume server recursion exists.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/core/page/transclusion/transclusion.service.ts

@@ -395,6 +395,15 @@ export class TransclusionService {
    * pages return `no_access`, missing/deleted pages return `not_found`. Does NOT
    * require `is_template` — any accessible page can be embedded (the template
    * flag only affects picker discovery).
+   *
+   * FLAT, single-level by design: this returns each requested page's own content
+   * verbatim and never recurses. If a returned page itself contains a `pageEmbed`
+   * node pointing at another page, that embed is left unresolved — the client
+   * issues a follow-up lookup for it. Because there is no server-side recursive
+   * expansion, there is no server depth/cycle to guard here: the embed depth/cycle
+   * cap (PAGE_EMBED_MAX_DEPTH) is purely a client RENDER concern. A scripted client
+   * that walks the graph manually is bounded by the per-user throttle (30/60s) on
+   * the controller plus the DTO's ArrayMaxSize(50) per call.
    */
   async lookupTemplate(
     sourcePageIds: string[],