fix: pre-landing review fixes for the Aside-first branch

Review army + adversarial passes (Claude and Codex) on the merged branch:

setup
- _prune_stale_generated scans the host dirs too (the generator already
  removed the render before setup ran, so the host branch was dead), skips
  symlinks in the render tree (rm -rf on a slash-terminated link empties its
  target), removes a host symlink only when it resolves into gstack, cleans a
  bannered real dir through _cleanup_weak_dir, recognizes frontmatter-renamed
  skills, and logs through log. The always-run codex render passes every host
  dir that may link to it.
- NEEDS_BUILD checks all three binaries (with $_EXE) and lib/ sources; the
  browser hint and the bootstrap summary honor GSTACK_SKIP_ASIDE, treat a
  requested skip as a request, and derive one skill list.

lib/aside-render.ts + bin/gstack-render.ts
- The loopback server carries a per-render secret path, checks containment on
  the real path (symlink escapes are 403), and rejects malformed encoding.
- Inline eval results are one base64 line, so page text cannot forge
  ASIDE_DIR= or the sentinel; the last ASIDE_DIR wins.
- runProc escalates SIGTERM to SIGKILL, bounds every wait, and clears every
  timer (an uncleared one kept gstack-render alive after printing OK).
- renderTmpDir refuses a shared /tmp name owned by someone else; the work dir
  and server are created inside try; goto's budget follows the render budget.
- probeAside classifies a present-but-failing CLI as ASIDE_NOT_RUNNING like
  the skills' bash probe; render() retries on gstack's own browser when Aside
  could not start or its private CDP bridge is gone (never on a page error
  or a timeout of a running script); the CLI reports the engine that actually
  rendered, exits 0 on --help, rejects non-numeric flags, documents
  --wait-timeout, fences EVAL/PAGE_ERRORS as untrusted content, and names the
  daemon's cookie-import JS lock remedy.
- The browse path passes --scale only when asked (a scale change rebuilds
  the daemon context) and restores the viewport after a sized screenshot.

resolvers / templates
- The bash probe honors GSTACK_SKIP_ASIDE and has a perl deadline on stock
  macOS; .local is no longer LOCAL (mDNS); same-origin filters compare parsed
  origins; link status is HEAD-checked only on LOCAL targets; every
  aside exec goes through the receipted _aside_exec prelude
  ({{ASIDE_EXEC_PRELUDE}}), including nine template blocks that called it
  bare; the design sketch and diagram staging use private directories.
- The generator prunes only bannered renders and never a host whose
  generation failed.

Docs, stale comments and dead code cleaned; goldens re-rendered; tests
updated and added for every behavior above.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

setup-deploy/SKILL.md

@@ -407,7 +407,8 @@ A step sometimes requires action on an external website the user controls: regis
 
    ```bash
    _T=""; command -v gtimeout >/dev/null 2>&1 && _T="gtimeout 30"; [ -z "$_T" ] && command -v timeout >/dev/null 2>&1 && _T="timeout 30"
-   if ! command -v aside >/dev/null 2>&1; then
+   [ -z "$_T" ] && command -v perl >/dev/null 2>&1 && _T="perl -e alarm(shift);exec(@ARGV) 30"
+   if [ "${GSTACK_SKIP_ASIDE:-}" = "1" ] || ! command -v aside >/dev/null 2>&1; then
      echo "NEEDS_ASIDE"
    elif $_T aside repl 'console.log("ASIDE_READY " + pwd)' 2>&1 | grep -q '^ASIDE_READY'; then
      echo "READY: aside $(aside --version 2>/dev/null)"