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/BOUNDARY.md

@@ -38,7 +38,6 @@ Only these types may cross the host-SX boundary:
 | list | `list` | `Array` | `Vec<SxValue>` |
 | dict | `dict` | `Object` / `Map` | `HashMap<String, SxValue>` |
 | sx-source | `SxExpr` wrapper | `string` | `String` |
-| style-value | `StyleValue` | `StyleValue` | `StyleValue` |
 
 **NOT allowed:** ORM models, datetime objects, request objects, raw callables, framework types. Convert at the edge before crossing.