Spec URL evaluation in router.sx, bootstrap to Python/JS

Add url-to-expr, auto-quote-unknowns, prepare-url-expr to router.sx —
the canonical URL-to-expression pipeline. Dots→spaces, parse, then
auto-quote unknown symbols as strings (slugs). The same spec serves
both server (Python) and client (JS) route handling.

- router.sx: three new pure functions for URL evaluation
- bootstrap_py.py: auto-include router module with html adapter
- platform_js.py: export urlToExpr/autoQuoteUnknowns/prepareUrlExpr
- sx_router.py: replace hand-written auto_quote_slugs with bootstrapped
  prepare_url_expr — delete ~50 lines of hardcoded function name sets
- Rebootstrap sx_ref.py (4331 lines) and sx-browser.js

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

shared/static/scripts/sx-browser.js

@@ -14,7 +14,7 @@
   // =========================================================================
 
   var NIL = Object.freeze({ _nil: true, toString: function() { return "nil"; } });
-  var SX_VERSION = "2026-03-12T22:27:08Z";
+  var SX_VERSION = "2026-03-12T22:55:39Z";
 
   function isNil(x) { return x === NIL || x === null || x === undefined; }
   function isSxTruthy(x) { return x !== false && !isNil(x); }
@@ -3922,6 +3922,30 @@ callExpr.push(dictGet(kwargs, k)); } }
   return (isSxTruthy((get(parsed, "type") == "special-form")) ? get(parsed, "inner") : NIL);
 })(); };
 
+  // url-to-expr
+  var urlToExpr = function(urlPath) { return (isSxTruthy(sxOr((urlPath == "/"), isEmpty(urlPath))) ? [] : (function() {
+  var trimmed = (isSxTruthy(startsWith(urlPath, "/")) ? slice(urlPath, 1) : urlPath);
+  return (function() {
+  var sxSource = replace_(trimmed, ".", " ");
+  return (function() {
+  var exprs = sxParse(sxSource);
+  return (isSxTruthy(isEmpty(exprs)) ? [] : first(exprs));
+})();
+})();
+})()); };
+
+  // auto-quote-unknowns
+  var autoQuoteUnknowns = function(expr, env) { return (isSxTruthy(!isSxTruthy(isList(expr))) ? expr : (isSxTruthy(isEmpty(expr)) ? expr : cons(first(expr), map(function(child) { return (isSxTruthy(isList(child)) ? autoQuoteUnknowns(child, env) : (isSxTruthy((typeOf(child) == "symbol")) ? (function() {
+  var name = symbolName(child);
+  return (isSxTruthy(sxOr(envHas(env, name), startsWith(name, ":"), startsWith(name, "~"), startsWith(name, "!"))) ? child : name);
+})() : child)); }, rest(expr))))); };
+
+  // prepare-url-expr
+  var prepareUrlExpr = function(urlPath, env) { return (function() {
+  var expr = urlToExpr(urlPath);
+  return (isSxTruthy(isEmpty(expr)) ? expr : autoQuoteUnknowns(expr, env));
+})(); };
+
 
   // === Transpiled from signals (reactive signal runtime) ===
 
@@ -6300,6 +6324,9 @@ return (isSxTruthy((_batchDepth == 0)) ? (function() {
     parseRoutePattern: parseRoutePattern,
     matchRoute: matchRoute,
     findMatchingRoute: findMatchingRoute,
+    urlToExpr: urlToExpr,
+    autoQuoteUnknowns: autoQuoteUnknowns,
+    prepareUrlExpr: prepareUrlExpr,
     registerIo: typeof registerIoPrimitive === "function" ? registerIoPrimitive : null,
     registerIoDeps: typeof registerIoDeps === "function" ? registerIoDeps : null,
     asyncRender: typeof asyncSxRenderWithEnv === "function" ? asyncSxRenderWithEnv : null,