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/eval.sx

@@ -143,7 +143,6 @@
               (= name "defcomp")     (sf-defcomp args env)
               (= name "defmacro")    (sf-defmacro args env)
               (= name "defstyle")    (sf-defstyle args env)
-              (= name "defkeyframes") (sf-defkeyframes args env)
               (= name "defhandler")  (sf-defhandler args env)
               (= name "defpage")     (sf-defpage args env)
               (= name "defquery")    (sf-defquery args env)
@@ -559,23 +558,13 @@
 
 (define sf-defstyle
   (fn (args env)
-    ;; (defstyle name expr) — bind name to evaluated expr (typically a StyleValue)
+    ;; (defstyle name expr) — bind name to evaluated expr (string, function, etc.)
     (let ((name-sym (first args))
           (value    (trampoline (eval-expr (nth args 1) env))))
       (env-set! env (symbol-name name-sym) value)
       value)))
 
 
-(define sf-defkeyframes
-  (fn (args env)
-    ;; (defkeyframes name (selector body) ...) — build @keyframes rule,
-    ;; register in keyframes dict, return StyleValue.
-    ;; Delegates to platform: build-keyframes returns a StyleValue.
-    (let ((kf-name (symbol-name (first args)))
-          (steps   (rest args)))
-      (build-keyframes kf-name steps env))))
-
-
 (define sf-begin
   (fn (args env)
     (if (empty? args)
@@ -931,9 +920,6 @@
 ;;   (zip lists...)           → list of tuples
 ;;
 ;;
-;; CSSX (style system):
-;;   (build-keyframes name steps env) → StyleValue (platform builds @keyframes)
-;;
 ;; Dynamic wind (for dynamic-wind):
 ;;   (push-wind! before after)  → void (push wind record onto stack)
 ;;   (pop-wind!)                → void (pop wind record from stack)