feat(gitsync): auto-bootstrap tom wiki från remote live-gren

Ett repo utan commits adopterar origin/<live_branch> automatiskt vid
första bakgrundssynken — färsk instans behöver ingen manuell reset.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/internal/graph/gitsync.go

@@ -186,6 +186,20 @@ func (s *Server) backgroundSync() {
 		record(fmt.Errorf("fetch: %w", err), false)
 		return
 	}
+	// Bootstrap: an empty wiki (no commits yet) adopts the remote live
+	// branch automatically, so a fresh instance needs no manual reset.
+	if !repo.HasCommits() {
+		if repo.RemoteBranchExists(gs.LiveBranch) {
+			_, err := repo.ResetToRemote(gs.LiveBranch, syncAuthor, syncEmail)
+			if err != nil {
+				record(fmt.Errorf("bootstrap från remote: %w", err), true)
+			} else {
+				log.Printf("[gitsync] empty wiki bootstrapped from origin/%s", gs.LiveBranch)
+				record(nil, false)
+			}
+			return
+		}
+	}
 	current, err := repo.CurrentBranch()
 	if err != nil || current != gs.LiveBranch {
 		// Someone is working on another branch; leave it alone.