feat(git-sync): native GitmostDataSource + 'git-sync' provenance (Phase A.4a)

Native data plane for git-sync (plan §3, §8.1):
- provenance: widen actor to 'user'|'agent'|'git-sync' (jwt-payload,
  auth-provenance decorator); PersistenceExtension resolves lastUpdatedSource
  with precedence agent > git-sync > user, debounced history (like a human edit,
  not the agent's immediate snapshot).
- GitmostDataSourceService implements @docmost/git-sync's GitSyncClient natively:
  reads via PageRepo/SpaceRepo (listSpaceTree complete:true, getPageJson), writes
  via PageService (create/removePage soft-delete/movePage with computed fractional
  position/update-rename/restore) + the writeBody linchpin through collab
  openDirectConnection('page.'+id, {actor:'git-sync'}) mirroring
  collaboration.handler withYdocConnection 'replace'. bind({workspaceId,userId})
  returns the context-bound client for the orchestrator.
- 10 unit/contract tests (mapping + soft-delete + move-position), tsc clean.

Known gap (closed in A.4b): PageService.create/update/movePage only branch on
actor==='agent'; git-sync provenance is already passed through so the row source
marker propagates once PageService honors 'git-sync'. Module/orchestrator/config
come next.

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

apps/server/src/collaboration/extensions/persistence.extension.ts

@@ -52,7 +52,12 @@ export function resolveSource(
   stickyTouched: boolean,
   contextActor?: string,
 ): ProvenanceSource {
-  return stickyTouched || contextActor === 'agent' ? 'agent' : 'user';
+  // Precedence: agent > git-sync > user. The sticky agent marker wins so a
+  // window that mixed an agent edit stays tagged 'agent'; otherwise a native
+  // git-sync write (plan §8.1) tags 'git-sync'; a plain human edit stays 'user'.
+  if (stickyTouched || contextActor === 'agent') return 'agent';
+  if (contextActor === 'git-sync') return 'git-sync';
+  return 'user';
 }
 
 /**
@@ -176,6 +181,9 @@ export class PersistenceExtension implements Extension {
     // Sticky agent marker: 'agent' if any agent edit landed in this window, OR
     // if the current writer is the agent (covers a store with no prior onChange
     // agent event in the same window). §15 H2.
+    // Provenance precedence: agent > git-sync > user (see resolveSource). A
+    // 'git-sync' store is NOT given an immediate history snapshot — it is
+    // debounced like a human edit (git-sync writes are full-body replaces).
     const lastUpdatedSource = resolveSource(
       this.consumeAgentTouched(documentName),
       context?.actor,