Remove CSSX style dictionary infrastructure — styling is just components

The entire parallel CSS system (StyleValue type, style dictionary,
keyword atom resolver, content-addressed class generation, runtime
CSS injection, localStorage caching) was built but never adopted —
the codebase already uses :class strings with defcomp components
for all styling. Remove ~3,000 lines of unused infrastructure.

Deleted:
- cssx.sx spec module (317 lines)
- style_dict.py (782 lines) and style_resolver.py (254 lines)
- StyleValue type, defkeyframes special form, build-keyframes platform fn
- Style dict JSON delivery (<script type="text/sx-styles">), cookies, localStorage
- css/merge-styles primitives, inject-style-value, fnv1a-hash platform interface

Simplified:
- defstyle now binds any value (string, function) — no StyleValue type needed
- render-attrs no longer special-cases :style StyleValue → class conversion
- Boot sequence skips style dict init step

Preserved:
- tw.css parsing + CSS class delivery (SX-Css headers, <style id="sx-css">)
- All component infrastructure (defcomp, caching, bundling, deps)
- defstyle as a binding form for reusable class strings

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

shared/sx/ref/special-forms.sx

@@ -363,20 +363,12 @@
 ;; --------------------------------------------------------------------------
 
 (define-special-form "defstyle"
-  :syntax (defstyle name atoms ...)
-  :doc "Define a named style. Evaluates atoms to a StyleValue and binds
-        it to name in the environment."
+  :syntax (defstyle name expr)
+  :doc "Define a named style value. Evaluates expr and binds the result
+        to name in the environment. The value is typically a class string
+        or a function that returns class strings."
   :tail-position "none"
-  :example "(defstyle card-style :rounded-lg :shadow-md :p-4 :bg-white)")
-
-(define-special-form "defkeyframes"
-  :syntax (defkeyframes name steps ...)
-  :doc "Define a CSS @keyframes animation. Steps are (percentage properties ...)
-        pairs. Produces a StyleValue with the animation name and keyframe rules."
-  :tail-position "none"
-  :example "(defkeyframes fade-in
-  (0   :opacity-0)
-  (100 :opacity-100))")
+  :example "(defstyle card-style \"rounded-lg shadow-md p-4 bg-white\")")
 
 (define-special-form "defhandler"
   :syntax (defhandler name (&key params ...) body)