Implement CSSX Phase 2: native SX style primitives

Replace Tailwind class strings with native SX expressions:
(css :flex :gap-4 :hover:bg-sky-200) instead of :class "flex gap-4 ..."

- Add style_dict.py: 516 atoms, variants, breakpoints, keyframes, patterns
- Add style_resolver.py: memoized resolver with variant splitting
- Add StyleValue type to types.py (frozen dataclass with class_name, declarations, etc.)
- Add css and merge-styles primitives to primitives.py
- Add defstyle and defkeyframes special forms to evaluator.py and async_eval.py
- Integrate StyleValue into html.py and async_eval.py render paths
- Add register_generated_rule() to css_registry.py, fix media query selector
- Add style dict JSON delivery with localStorage caching to helpers.py
- Add client-side css primitive, resolver, and style injection to sx.js

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

shared/sx/html.py

@@ -27,7 +27,7 @@ from __future__ import annotations
 import contextvars
 from typing import Any
 
-from .types import Component, Keyword, Lambda, Macro, NIL, Symbol
+from .types import Component, Keyword, Lambda, Macro, NIL, StyleValue, Symbol
 from .evaluator import _eval as _raw_eval, _call_component as _raw_call_component, _expand_macro, _trampoline
 
 def _eval(expr, env):
@@ -479,6 +479,19 @@ def _render_element(tag: str, args: list, env: dict[str, Any]) -> str:
             children.append(arg)
             i += 1
 
+    # Handle :style StyleValue — convert to class and register CSS rule
+    style_val = attrs.get("style")
+    if isinstance(style_val, StyleValue):
+        from .css_registry import register_generated_rule
+        register_generated_rule(style_val)
+        # Merge into :class
+        existing_class = attrs.get("class")
+        if existing_class and existing_class is not NIL and existing_class is not False:
+            attrs["class"] = f"{existing_class} {style_val.class_name}"
+        else:
+            attrs["class"] = style_val.class_name
+        del attrs["style"]
+
     # Collect CSS classes if collector is active
     class_val = attrs.get("class")
     if class_val is not None and class_val is not NIL and class_val is not False: