Remove old CSSX system — ~tw is the sole CSS engine

Phase 1 Step 1 of the architecture roadmap. The old cssx.sx
(cssx-resolve, cssx-process-token, cssx-template, old tw function)
is superseded by the ~tw component system in tw.sx.

- Delete shared/sx/templates/cssx.sx
- Remove cssx.sx from all load lists (sx_server.ml, run_tests.ml,
  mcp_tree.ml, compile-modules.js, bundle.sh, sx-build-all.sh)
- Replace (tw "tokens") inline style calls with (~tw :tokens "tokens")
  in layouts.sx and not-found.sx
- Remove _css-hash / init-css-tracking / SX-Css header plumbing
  (dead code — ~tw/flush + flush-collected-styles handle CSS now)
- Remove sx-css-classes param and meta tag from shell template
- Update stale data-cssx references to data-sx-css in tests

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

hosts/ocaml/bin/mcp_tree.ml

@@ -609,7 +609,7 @@ let rec handle_tool name args =
       "render.sx"; "core-signals.sx"; "signals.sx"; "deps.sx"; "router.sx";
       "page-helpers.sx"; "freeze.sx"; "bytecode.sx"; "compiler.sx"; "vm.sx";
       "dom.sx"; "browser.sx"; "adapter-html.sx"; "adapter-sx.sx"; "adapter-dom.sx";
-      "cssx.sx"; "tw-layout.sx"; "tw-type.sx"; "tw.sx";
+      "tw-layout.sx"; "tw-type.sx"; "tw.sx";
       "boot-helpers.sx"; "hypersx.sx"; "harness.sx"; "harness-reactive.sx";
       "harness-web.sx"; "engine.sx"; "orchestration.sx"; "boot.sx";
     ] in

hosts/ocaml/bin/run_tests.ml

@@ -1168,7 +1168,6 @@ let run_spec_tests env test_files =
   load_module "tw.sx" templates_dir;
   load_module "tw-layout.sx" templates_dir;
   load_module "tw-type.sx" templates_dir;
-  load_module "cssx.sx" templates_dir;
   (* SX docs site: components, handlers, demos *)
   let sx_comp_dir = Filename.concat project_dir "sx/sxc" in
   let sx_sx_dir = Filename.concat project_dir "sx/sx" in

hosts/ocaml/bin/sx_server.ml

@@ -1657,7 +1657,6 @@ let http_render_page env path headers =
             Keyword "component-hash"; get_shell "component-hash";
             Keyword "pages-sx"; get_shell "pages-sx";
             Keyword "sx-css"; get_shell "sx-css";
-            Keyword "sx-css-classes"; get_shell "sx-css-classes";
             Keyword "asset-url"; get_shell "asset-url";
             Keyword "wasm-hash"; get_shell "wasm-hash";
             Keyword "platform-hash"; get_shell "platform-hash";
@@ -1771,7 +1770,6 @@ let http_inject_shell_statics env static_dir sx_sxc =
     Filename.dirname (Filename.dirname static_dir) in
   let templates_dir = project_dir ^ "/shared/sx/templates" in
   let client_libs = [
-    templates_dir ^ "/cssx.sx";
     templates_dir ^ "/tw-layout.sx";
     templates_dir ^ "/tw-type.sx";
     templates_dir ^ "/tw.sx";
@@ -1860,7 +1858,6 @@ let http_inject_shell_statics env static_dir sx_sxc =
     (List.length (String.split_on_char '\n' pages_sx));
   ignore (env_bind env "__shell-pages-sx" (String pages_sx));
   ignore (env_bind env "__shell-sx-css" (String sx_css));
-  ignore (env_bind env "__shell-sx-css-classes" (String ""));
   ignore (env_bind env "__shell-asset-url" (String "/static"));
   ignore (env_bind env "__shell-wasm-hash" (String wasm_hash));
   ignore (env_bind env "__shell-platform-hash" (String platform_hash));

hosts/ocaml/browser/bundle.sh

@@ -66,8 +66,7 @@ cp "$ROOT/web/engine.sx"        "$DIST/sx/"
 cp "$ROOT/web/orchestration.sx" "$DIST/sx/"
 cp "$ROOT/web/boot.sx"          "$DIST/sx/"
 
-# 9. Styling (tw token engine + legacy cssx)
-cp "$ROOT/shared/sx/templates/cssx.sx"      "$DIST/sx/"
+# 9. Styling (tw token engine)
 cp "$ROOT/shared/sx/templates/tw-layout.sx" "$DIST/sx/"
 cp "$ROOT/shared/sx/templates/tw-type.sx"   "$DIST/sx/"
 cp "$ROOT/shared/sx/templates/tw.sx"        "$DIST/sx/"

hosts/ocaml/browser/compile-modules.js

@@ -37,7 +37,7 @@ const FILES = [
   'render.sx', 'core-signals.sx', 'signals.sx', 'deps.sx', 'router.sx',
   'page-helpers.sx', 'freeze.sx', 'bytecode.sx', 'compiler.sx', 'vm.sx',
   'dom.sx', 'browser.sx', 'adapter-html.sx', 'adapter-sx.sx', 'adapter-dom.sx',
-  'cssx.sx', 'tw-layout.sx', 'tw-type.sx', 'tw.sx',
+  'tw-layout.sx', 'tw-type.sx', 'tw.sx',
   'boot-helpers.sx', 'hypersx.sx', 'harness.sx', 'harness-reactive.sx',
   'harness-web.sx', 'engine.sx', 'orchestration.sx', 'boot.sx',
 ];