host: revert legacy-editor shims — clean over fancy, 181/181

Pull out the debt that revived the legacy editor: removed kg-compat.sx (uncommitted
bare->namespaced kg-card aliases), the ./blog container mount, the legacy
sx-editor.js + hardcoded asset URLs + ~editor/sx-editor-styles reuse at /new, and
the blog/sx preloads. /new is now a clean minimal form.

Finding that reshapes Phase 5: render-page (5.1) renders STATIC component trees
but is NOT the full evaluator — a component with a data loop ((map fn items) over
(unquote data)) errors 'Not callable: nil'. So clean dynamic component pages + a
native island editor need the aser SSR pipeline (5.2), not just render-page.

Posts still render via per-block guarded render-page; unsupported editor cards
(~kg-md) show placeholders by design (no alias shim). All endpoints 200, boot clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.dev-sx-host.yml

@@ -28,9 +28,6 @@ services:
       - ./spec:/app/spec:ro
       - ./lib:/app/lib:ro
       - ./web:/app/web:ro
-      # blog app SX — reused for the editor's style component (transitional;
-      # retire when the editor + its styles are host-owned / asset-managed)
-      - ./blog:/app/blog:ro
       # OCaml server binary — this worktree's build (has the SX_HTTP_HOST bind fix)
       - ./hosts/ocaml/_build/default/bin/sx_server.exe:/app/bin/sx_server:ro
       # Durable persist store (the SX op-log/kv on disk) — survives restarts.