feat(editor): page templates - live whole-page embed (MVP)

Embed another page's LIVE content into a host page (it updates when the source
changes, not a static copy). A page can be flagged a template for discovery in
the picker; any accessible page can be embedded.

Server:
- migrations: pages.is_template (+ partial index) and page_template_references
  (whole-page back-refs); db.d.ts/entity types hand-merged (db.d.ts is curated).
- POST /pages/toggle-template (CASL Edit) flips is_template; is_template is
  returned by findById + the sidebar tree select so the tree menu label
  reflects state. Search suggestions gain an onlyTemplates filter for the picker.
- POST /pages/template/lookup ({sourcePageIds[]}, <=50): returns each accessible
  source's {title, icon, slugId, content, sourceUpdatedAt} with comment marks
  stripped (same access path as transclusion: filterViewerAccessiblePageIds;
  inaccessible -> no_access, missing -> not_found; error path -> not_found, never
  raw content).
- reference sync (collectPageEmbedsFromPmJson + syncPageTemplateReferences) on
  the Yjs save hook; duplicatePage remaps pageEmbed.sourcePageId + inserts refs.
  Known MVP gap: REST content updates don't resync refs (lookup uses in-doc ids).

Client:
- pageEmbed node (editor-ext, registered in BOTH client + server schemas);
  read-only NodeView with a batching lookup; '/Embed page' slash + template
  picker (self-embed prevented); 'Make/Unset template' in the tree node menu.
- Cycle guard: an ancestry-chain context + depth cap (5) render a 'circular
  embed' placeholder instead of recursing.
- Public shares show a placeholder (no public lookup in MVP).

MVP excludes (follow-ups): public-share lookup, unsync->static copy, server-side
expansion for export/RAG, MCP schema mirror, point-in-time snapshots.

Implements docs/page-templates-plan.md (MVP, variant A).

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

apps/server/src/database/database.module.ts

@@ -13,6 +13,7 @@ import { PagePermissionRepo } from './repos/page/page-permission.repo';
 import { CommentRepo } from './repos/comment/comment.repo';
 import { PageTransclusionsRepo } from './repos/page-transclusions/page-transclusions.repo';
 import { PageTransclusionReferencesRepo } from './repos/page-transclusions/page-transclusion-references.repo';
+import { PageTemplateReferencesRepo } from './repos/page-template-references/page-template-references.repo';
 import { PageHistoryRepo } from './repos/page/page-history.repo';
 import { AttachmentRepo } from './repos/attachment/attachment.repo';
 import { KyselyDB } from '@docmost/db/types/kysely.types';
@@ -85,6 +86,7 @@ import { normalizePostgresUrl } from '../common/helpers';
     PagePermissionRepo,
     PageTransclusionsRepo,
     PageTransclusionReferencesRepo,
+    PageTemplateReferencesRepo,
     PageHistoryRepo,
     CommentRepo,
     FavoriteRepo,
@@ -115,6 +117,7 @@ import { normalizePostgresUrl } from '../common/helpers';
     PagePermissionRepo,
     PageTransclusionsRepo,
     PageTransclusionReferencesRepo,
+    PageTemplateReferencesRepo,
     PageHistoryRepo,
     CommentRepo,
     FavoriteRepo,