docs(controller-peers-env-fallback): design re-validation fixes

Iterated design review until clean (GO):

- Controller main() calls mylog_fini() before every early return, so
  log lines written by tlog's background thread survive the exit.
- cluster_init_phase1() keeps its candidates_count > 0 guard around the
  new xce_peers_find_identity() call (standalone stays my_priority 0).
- xceadmin adds the "(from $VAR)" source note only to network errors,
  not to local cluster-bin file errors (OSError with filename set).
- Regression script: scratch --workdir/--certdir/--logfile per daemon,
  refuses to run if a local cluster is up (port 9990, worker socket),
  --sim case asserts the sim branch ran, 2.3 patches follow_redirects,
  2.8 malformed-entry cases use a readable cluster-bin file, wrapper
  test expects PEERS_STR form.
- Two existing scripts that start xce_scheduler without --peers will
  unset XCE_CONTROLLER_PEERS; --interactive wording corrected.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.kiro/specs/controller-peers-env-fallback/spec.json

@@ -1,7 +1,7 @@
 {
   "feature_name": "controller-peers-env-fallback",
   "created_at": "2026-09-22T07:37:10Z",
-  "updated_at": "2026-10-03T04:05:28Z",
+  "updated_at": "2026-10-03T04:45:21Z",
   "language": "en",
   "phase": "design-generated",
   "approvals": {