Add Bootstrappers section, essays index, specs prose, layout fixes

- New Bootstrappers top-level section with overview index and JS bootstrapper
  page that runs bootstrap_js.py and displays both source and generated output
  with live script injection (full page load, not SX navigation)
- Essays section: index page with linked cards and summaries, sx-sucks moved
  to end of nav, removed "grand tradition" line
- Specs: English prose descriptions alongside all canonical .sx specs, added
  Boot/CSSX/Browser spec files to architecture page
- Layout: menu bar nav items wrap instead of overflow, baseline alignment
  between label and nav options
- Homepage: added copyright line

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sx/layouts.sx

@@ -11,8 +11,9 @@
            (dict :label "Reference" :href "/reference/")
            (dict :label "Protocols" :href "/protocols/wire-format")
            (dict :label "Examples" :href "/examples/click-to-load")
-           (dict :label "Essays" :href "/essays/sx-sucks")
-           (dict :label "Specs" :href "/specs/"))))
+           (dict :label "Essays" :href "/essays/")
+           (dict :label "Specs" :href "/specs/")
+           (dict :label "Bootstrappers" :href "/bootstrappers/"))))
     (<> (map (lambda (item)
       (~nav-link
         :href (get item "href")