Add header and event detail pages, fix copyright, rename essay

- Detail pages for all 18 HTTP headers with descriptions, example usage,
  direction badges (request/response/both), and live demos for SX-Prompt,
  SX-Trigger, SX-Retarget
- Detail pages for all 10 DOM events with descriptions, example usage,
  and live demos for beforeRequest, afterSettle, responseError,
  validationFailed
- Header and event table rows now link to their detail pages
- Fix copyright symbol on home page (was literal \u00a9, now actual ©)
- Rename "Godel, Escher, Bach" essay to "Strange Loops" with updated summary
- Remove duplicate script injection from bootstrapper page

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

sx/sx/nav-data.sx

@@ -71,8 +71,8 @@
         :summary "How SX implements proper tail calls via trampolining in a language that doesn't have them.")
   (dict :label "Continuations" :href "/essays/continuations"
         :summary "First-class continuations in a tree-walking evaluator — theory and implementation.")
-  (dict :label "Godel, Escher, Bach" :href "/essays/godel-escher-bach"
-        :summary "Self-reference, strange loops, and what a self-hosting language has to do with GEB.")
+  (dict :label "Strange Loops" :href "/essays/godel-escher-bach"
+        :summary "Self-reference, and the tangled hierarchy of a language that defines itself.")
   (dict :label "The Reflexive Web" :href "/essays/reflexive-web"
         :summary "A web where pages can inspect, modify, and extend their own rendering pipeline.")
   (dict :label "sx sucks" :href "/essays/sx-sucks"