v0.6.5: Renderer pipeline, docs rewrite, architecture diagrams

Lift block rendering to kernel SDK primitives (sw.renderers + sw.markdown)
so all surfaces share one markdown pipeline. Rewrite docs for external
audience — remove all fork history references. Add Mermaid architecture
diagrams, CONTRIBUTING guide, and extension tutorial.

- sw.renderers SDK module: kernel-level renderer registry
- sw.markdown SDK module: unified marked v16 + DOMPurify pipeline
- Browser extension script loader for renderer injection
- Notes + Docs surfaces migrated to sw.markdown.renderSync()
- 4 renderer extensions rewritten to IIFE + sw.renderers.register()
- 6 Mermaid diagrams in ARCHITECTURE.md
- CONTRIBUTING.md + TUTORIAL-FIRST-EXTENSION.md
- DESIGN-WORKFLOWS.md replaces fork-era design doc
- Surface alias routes removed from main.go
- ICD/SDK runners migrated to /admin/packages/ endpoints
- 13 new renderer tests
- Docs, CHANGELOG, ROADMAP cleaned of fork references

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/pages/templates/base.html

@@ -21,7 +21,7 @@
     <link rel="stylesheet" href="{{.BasePath}}/css/extension-surface.css?v={{.Version}}">
     <link rel="stylesheet" href="{{.BasePath}}/css/sw-shell.css?v={{.Version}}">
     <link rel="stylesheet" href="{{.BasePath}}/css/sw-debug.css?v={{.Version}}">
-    {{/* gutted: css-chat, css-notes, css-projects templates removed */}}
+    {{/* css-chat, css-notes, css-projects templates removed — surfaces provide their own styles */}}
     {{/* v0.27.0: Extension surface CSS — loaded from /surfaces/{id}/css/main.css */}}
     {{if and .Manifest (eq .Manifest.Source "extension")}}
     <link rel="stylesheet" href="{{.BasePath}}/surfaces/{{.Surface}}/css/main.css?v={{.Version}}">
@@ -117,9 +117,8 @@
         {{if .Manifest}}window.__MANIFEST__ = {{.Manifest | toJSON}};{{end}}
     </script>
 
-    {{/* v0.37.14 Scorched Earth IV: sb.js, events.js, switchboard-sdk.js,
-         workflow-surfaces.js removed. All surfaces use Preact SDK boot().
-         Survivors: debug.js, repl.js (standalone, no old-layer deps). */}}
+    {{/* All surfaces use Preact SDK boot(). Legacy script includes removed.
+         Standalone utils: debug.js, repl.js (no SDK dependencies). */}}
 
     {{if eq .Surface "admin"}}{{template "scripts-admin" .}}{{end}}
     {{if eq .Surface "team-admin"}}{{template "scripts-team-admin" .}}{{end}}
@@ -142,6 +141,12 @@
     </script>
     {{end}}
 
+    {{/* v0.6.5: Browser-tier extension scripts (renderers, etc.)
+         Loaded after surface scripts so sw:ready fires first. */}}
+    {{range .BrowserExtensions}}
+    <script nonce="{{$.CSPNonce}}" src="{{$.BasePath}}/surfaces/{{.}}/js/script.js?v={{$.Version}}"></script>
+    {{end}}
+
     {{/* v0.37.13: Legacy UserMenu hydration removed — all surfaces use Preact UserMenu. */}}
 
     {{/* ── Debug Modal (Preact, v0.37.18) ───── */}}