admin: refresh stale ErrTablesNotLeader sentinel comment (Claude review)

Two nit follow-ups from Claude review #4 on 87043f9:

1) The ErrTablesNotLeader sentinel's own declaration comment still
   said "the future AdminForward RPC catches this as the trigger to
   forward". The previous review pass updated only the writeTablesError
   site comment. Refreshed the sentinel comment too: when a
   LeaderForwarder is configured, tryForwardCreate / tryForwardDelete
   catch this before writeTablesError; without a forwarder, the arm
   maps to 503 + Retry-After:1.

2) newFollowerHandler still constructed notLeaderSource with an empty
   tables map. notLeaderSource overrides AdminCreateTable /
   AdminDeleteTable to unconditionally return ErrTablesNotLeader, so
   the map is never consulted. The two individual tests cleaned up in
   the previous commit already use bare &notLeaderSource{}; the helper
   now matches.

Author: bootjp

internal/admin/dynamo_handler.go

@@ -119,8 +119,10 @@ var (
 	// role required for the operation. Maps to 403.
 	ErrTablesForbidden = errors.New("admin tables: principal lacks required role")
 	// ErrTablesNotLeader is returned when the local node is not the
-	// Raft leader. Maps to 503 + Retry-After: 1 today; the future
-	// AdminForward RPC catches this as the trigger to forward.
+	// Raft leader. When a LeaderForwarder is configured,
+	// tryForwardCreate / tryForwardDelete catch this before it reaches
+	// writeTablesError and forward the request to the leader
+	// transparently. Without a forwarder, maps to 503 + Retry-After: 1.
 	ErrTablesNotLeader = errors.New("admin tables: local node is not the raft leader")
 	// ErrTablesNotFound is returned when DELETE / DESCRIBE / a
 	// follow-up read targets a table that does not exist. Maps to

internal/admin/forward_integration_test.go

@@ -63,7 +63,10 @@ func (s *notLeaderSource) AdminDeleteTable(_ context.Context, _ AuthPrincipal, _
 
 func newFollowerHandler(t *testing.T, fwd LeaderForwarder) *DynamoHandler {
 	t.Helper()
-	src := &notLeaderSource{stubTablesSource: stubTablesSource{tables: map[string]*DynamoTableSummary{}}}
+	// notLeaderSource overrides the write methods to unconditionally
+	// return ErrTablesNotLeader, so the embedded stubTablesSource
+	// never reads its tables map.
+	src := &notLeaderSource{}
 	h := NewDynamoHandler(src)
 	if fwd != nil {
 		h = h.WithLeaderForwarder(fwd)