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/render.sx

@@ -74,7 +74,7 @@
 (define definition-form?
   (fn (name)
     (or (= name "define") (= name "defcomp") (= name "defmacro")
-        (= name "defstyle") (= name "defkeyframes") (= name "defhandler"))))
+        (= name "defstyle") (= name "defhandler"))))
 
 
 (define parse-element-args
@@ -116,9 +116,6 @@
                 ""
               ;; Nil values — skip
               (nil? val) ""
-              ;; StyleValue on :style → emit as class
-              (and (= key "style") (style-value? val))
-                (str " class=\"" (style-value-class val) "\"")
               ;; Normal attr
               :else (str " " key "=\"" (escape-attr (str val)) "\""))))
         (keys attrs)))))
@@ -202,10 +199,6 @@
 ;;   (escape-attr s)           → attribute-value-escaped string
 ;;   (raw-html-content r)      → unwrap RawHTML marker to string
 ;;
-;; StyleValue:
-;;   (style-value? x)          → boolean (is x a StyleValue?)
-;;   (style-value-class sv)    → string (CSS class name)
-;;
 ;; Serialization:
 ;;   (serialize val)           → SX source string representation of val
 ;;