Add on-demand CSS: registry, pre-computed component classes, header compression

- Parse tw.css into per-class lookup registry at startup
- Pre-scan component CSS classes at registration time (avoid per-request regex)
- Compress SX-Css header: 8-char hash replaces full class list (LRU cache)
- Add ;@css comment annotation for dynamically constructed class names
- Safelist bg-sky-{100..400} in Tailwind config for menu-row-sx dynamic shades
- Client sends/receives hash, falls back gracefully on cache miss

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

shared/sx/jinja_bridge.py

@@ -113,11 +113,25 @@ def register_components(sx_source: str) -> None:
     """
     from .evaluator import _eval
     from .parser import parse_all
+    from .css_registry import scan_classes_from_sx
+
+    # Snapshot existing component names before eval
+    existing = set(_COMPONENT_ENV.keys())
 
     exprs = parse_all(sx_source)
     for expr in exprs:
         _eval(expr, _COMPONENT_ENV)
 
+    # Pre-scan CSS classes for newly registered components.
+    # Scan the full source once — components from the same file share the set.
+    # Slightly over-counts per component but safe and avoids re-scanning at request time.
+    all_classes: set[str] | None = None
+    for key, val in _COMPONENT_ENV.items():
+        if key not in existing and isinstance(val, Component):
+            if all_classes is None:
+                all_classes = scan_classes_from_sx(sx_source)
+            val.css_classes = set(all_classes)
+
 
 # ---------------------------------------------------------------------------
 # sx() — render s-expression from Jinja template
@@ -232,6 +246,12 @@ def client_components_tag(*names: str) -> str:
     return f'<script type="text/sx" data-components>{source}</script>'
 
 
+def sx_css_all() -> str:
+    """Return all CSS rules (preamble + utilities) for Jinja fallback pages."""
+    from .css_registry import get_all_css
+    return get_all_css()
+
+
 def setup_sx_bridge(app: Any) -> None:
     """Register s-expression helpers with a Quart app's Jinja environment.
 
@@ -243,7 +263,9 @@ def setup_sx_bridge(app: Any) -> None:
     This registers:
     - ``sx(source, **kwargs)`` — sync render (components, pure HTML)
     - ``sx_async(source, **kwargs)`` — async render (with I/O resolution)
+    - ``sx_css_all()`` — full CSS dump for non-sx pages
     """
     app.jinja_env.globals["sx"] = sx
     app.jinja_env.globals["render"] = render
     app.jinja_env.globals["sx_async"] = sx_async
+    app.jinja_env.globals["sx_css_all"] = sx_css_all