Add comprehensive TW test suite (627 tests), fix 4 bugs, add 9 features

Bugs fixed:
- line-through: check full token not just head after hyphen split
- gap-x-N/gap-y-N: compound 2-part spacing prefix handler in tw-layout
- Negative values (-mt-4): replace ":" with ":-" instead of no-op
- Class name doubling: chain replace calls instead of concatenating

New features in tw-process-token:
- !important modifier (!p-4 → padding:1rem !important)
- dark: variant (class-based, .dark ancestor selector)
- group-hover:/group-focus:/group-active: (parent state)
- peer-focus:/peer-hover:/peer-checked:/peer-disabled: (sibling state)
- @container queries (@md:flex → @container(min-width:448px))
- Colour opacity modifier (bg-sky-500/50 → hsl with alpha)
- Ring colours (ring-sky-500 → --tw-ring-color)
- Arbitrary values (w-[300px], grid-cols-[1fr_2fr], bg-[#ff0000])
- colour-with-alpha helper for HSL+alpha generation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/javascript/run_tests.js

@@ -244,6 +244,20 @@ env["render-sx"] = function(source) {
   return parts.join("");
 };
 
+// Mock request/state primitives for test-handlers.sx
+const _mockState = {};
+env["now"] = function(fmt) { return new Date().toISOString(); };
+env["state-get"] = function(key, dflt) { return key in _mockState ? _mockState[key] : (dflt !== undefined ? dflt : null); };
+env["state-set!"] = function(key, val) { _mockState[key] = val; return val; };
+env["state-clear!"] = function(key) { delete _mockState[key]; return null; };
+env["request-method"] = function() { return "GET"; };
+env["request-arg"] = function(name, dflt) { return dflt !== undefined ? dflt : null; };
+env["request-form"] = function(name, dflt) { return dflt !== undefined ? dflt : ""; };
+env["request-headers-all"] = function() { return {}; };
+env["request-form-all"] = function() { return {}; };
+env["request-args-all"] = function() { return {}; };
+env["request-content-type"] = function() { return "text/html"; };
+
 // Platform test functions
 env["try-call"] = function(thunk) {
   try {
@@ -315,6 +329,33 @@ if (fs.existsSync(canonicalPath)) {
   }
 }
 
+// Load sx-swap.sx (needed by spec/tests/test-sx-swap.sx)
+const swapPath = path.join(projectDir, "lib", "sx-swap.sx");
+if (fs.existsSync(swapPath)) {
+  const swapSrc = fs.readFileSync(swapPath, "utf8");
+  const swapExprs = Sx.parse(swapSrc);
+  for (const expr of swapExprs) {
+    try { Sx.eval(expr, env); } catch (e) {
+      console.error(`Error loading sx-swap.sx: ${e.message}`);
+    }
+  }
+}
+
+// Load tw system (needed by spec/tests/test-tw.sx)
+const twDir = path.join(projectDir, "shared", "sx", "templates");
+for (const twFile of ["tw-type.sx", "tw-layout.sx", "tw.sx"]) {
+  const twPath = path.join(twDir, twFile);
+  if (fs.existsSync(twPath)) {
+    const twSrc = fs.readFileSync(twPath, "utf8");
+    const twExprs = Sx.parse(twSrc);
+    for (const expr of twExprs) {
+      try { Sx.eval(expr, env); } catch (e) {
+        console.error(`Error loading ${twFile}: ${e.message}`);
+      }
+    }
+  }
+}
+
 // Load compiler + VM from lib/ when running full tests
 if (fullBuild) {
   const libDir = path.join(projectDir, "lib");