Rewrite CSSX: unified Tailwind-style utility token system

Replace the three-layer cssx system (macro + value functions + class
components) with a single token resolver. Tokens like "bg-yellow-199",
"hover:bg-rose-500", "md:text-xl" are parsed into CSS declarations.

Two delivery mechanisms, same token format:
- tw() function: returns inline style string for :style
- ~cssx/tw macro: injects JIT class + <style> onto first child element

The resolver handles: colours (21 names, any shade 0-950), spacing,
typography, display, max-width, rounded, opacity, w/h, gap, text
decoration, cursor, overflow, transitions. States (hover/focus/active)
and responsive breakpoints (sm/md/lg/xl/2xl) for class-based usage.

Next step: replace macro/function approach with spec-level primitives
(defcontext/provide/context + spread) so ~cssx/tw becomes a proper
component returning spread values, with rules collected via context.

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

sx/sx/not-found.sx

@@ -2,19 +2,18 @@
 
 (defcomp ~not-found/content (&key (path :as string?))
   (div :class "max-w-3xl mx-auto px-4 py-12 text-center"
-    (h1 :style (cssx (:text (colour "stone" 800) (size "3xl") (weight "bold")))
+    (h1 :style (tw "text-stone-800 text-3xl font-bold")
       "404")
     (p :class "mt-4"
-       :style (cssx (:text (colour "stone" 500) (size "lg")))
+       :style (tw "text-stone-500 text-lg")
       "Page not found")
     (when path
       (p :class "mt-2"
-         :style (cssx (:text (colour "stone" 400) (size "sm") (family "mono")))
+         :style (tw "text-stone-400 text-sm font-mono")
         path))
     (a :href "/sx/"
        :sx-get "/sx/" :sx-target "#main-panel" :sx-select "#main-panel"
        :sx-swap "outerHTML" :sx-push-url "true"
        :class "inline-block mt-6 px-4 py-2 rounded border transition-colors"
-       :style (cssx (:text (colour "violet" 700) (size "sm"))
-                    (:border (colour "violet" 200)))
+       :style (tw "text-violet-700 text-sm border-violet-200")
       "Back to home")))