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/core/auth/dto/jwt-payload.ts

@@ -3,8 +3,12 @@
  * from the SIGNED token claim (never a request body), so 'agent' is unspoofable.
  * Single source of truth so a typo like 'agnet' can't slip through as a bare
  * string (#143 review). Distinct from `ActorType` (auth principal kind).
+ *
+ * 'git-sync' marks writes made by the git-sync data plane (plan §8.1). It NEVER
+ * travels in a user-facing token; it is set in-process on the collab connection
+ * context by the native datasource, so it cannot be spoofed from a request.
  */
-export type ProvenanceSource = 'user' | 'agent';
+export type ProvenanceSource = 'user' | 'agent' | 'git-sync';
 
 export enum JwtType {
   ACCESS = 'access',
@@ -26,7 +30,8 @@ export type JwtPayload = {
   // normal user token (treated as 'user'); set only when the internal agent
   // mints a provenance access token so REST writes (create/rename/move page,
   // comment create/resolve) record a non-spoofable 'agent' marker (§6.5 / §15
-  // C3 / §14 N2).
+  // C3 / §14 N2). (git-sync writes use the in-process actor, not a token — see
+  // the ProvenanceSource note.)
   actor?: ProvenanceSource;
   // Nullable: an external MCP agent has no internal ai_chats row, so it carries
   // an 'agent' actor with a null aiChatId.
@@ -39,7 +44,8 @@ export type JwtCollabPayload = {
   type: 'collab';
   // Optional agent-edit provenance, signed into the collab token. Absent for
   // the human collab path (treated as 'user'); set only when the internal agent
-  // mints a provenance collab token (§6.6 / §15 C2).
+  // mints a provenance collab token (§6.6 / §15 C2). 'git-sync' (in ProvenanceSource)
+  // is accepted for type-compatibility with the in-process git-sync write path.
   actor?: ProvenanceSource;
   // Nullable: an external MCP agent has no internal ai_chats row, so it carries
   // an 'agent' actor with a null aiChatId.