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/main.go

@@ -830,14 +830,6 @@ func main() {
 			admin.DELETE("/backups/:name", backupH.DeleteBackup)
 			admin.POST("/restore", backupH.RestoreBackup)
 
-			// Surface aliases (backward compat — same handlers)
-			admin.GET("/surfaces", pkgAdm.ListPackages)
-			admin.GET("/surfaces/:id", pkgAdm.GetPackage)
-			admin.POST("/surfaces/install", pkgAdm.InstallPackage)
-			admin.PUT("/surfaces/:id/enable", pkgAdm.EnablePackage)
-			admin.PUT("/surfaces/:id/disable", pkgAdm.DisablePackage)
-			admin.DELETE("/surfaces/:id", pkgAdm.DeletePackage)
-
 		}
 	}