Phase 8-9: Convert events + sx layouts, add missing JS primitives

Events (Phase 8):
- Create events/sx/layouts.sx with 18 defcomps for all 9 layout pairs
- Convert all layout functions to render_to_sx_with_env + _ctx_to_env
- Convert 5 render functions to eliminate root_header_sx calls
- Zero root_header_sx references remain in events

SX Docs (Phase 9):
- Create sx/sx/layouts.sx with layout defcomps
- Convert 4 layout functions to render_to_sx_with_env + _ctx_to_env

JS primitives:
- Add slice, replace, upper, lower, trim, escape, strip-tags, split,
  join, pluralize, clamp, parse-int, format-decimal, format-date,
  parse-datetime, split-ids, starts-with?, ends-with?, dissoc, into
- Fix contains? for strings (indexOf instead of in operator)
- Prevents "Undefined symbol" errors when .sx expressions using
  server-side primitives are evaluated client-side

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

shared/static/scripts/sx.js

@@ -320,6 +320,7 @@
   PRIMITIVES["last"] = function (c) { return c && c.length > 0 ? c[c.length - 1] : NIL; };
   PRIMITIVES["rest"] = function (c) { return c ? c.slice(1) : []; };
   PRIMITIVES["nth"] = function (c, n) { return c && n < c.length ? c[n] : NIL; };
+  PRIMITIVES["slice"] = function (c, start, end) { return c ? (end !== undefined && end !== NIL ? c.slice(start, end) : c.slice(start)) : c; };
   PRIMITIVES["cons"] = function (x, c) { return [x].concat(c || []); };
   PRIMITIVES["append"] = function (c, x) { return (c || []).concat([x]); };
   PRIMITIVES["keys"] = function (d) { return Object.keys(d || {}); };
@@ -340,6 +341,57 @@
     for (var i = a; step > 0 ? i < b : i > b; i += step) r.push(i);
     return r;
   };
+  PRIMITIVES["dissoc"] = function (d) {
+    var out = {}; for (var k in d) out[k] = d[k];
+    for (var i = 1; i < arguments.length; i++) delete out[arguments[i]];
+    return out;
+  };
+  PRIMITIVES["into"] = function (target, src) {
+    if (Array.isArray(target)) return target.concat(src || []);
+    var out = {}; for (var k in target) out[k] = target[k]; for (var k2 in src) out[k2] = src[k2]; return out;
+  };
+
+  // String operations
+  PRIMITIVES["replace"] = function (s, from, to) { return s ? String(s).split(from).join(to) : ""; };
+  PRIMITIVES["upper"] = function (s) { return s ? String(s).toUpperCase() : ""; };
+  PRIMITIVES["lower"] = function (s) { return s ? String(s).toLowerCase() : ""; };
+  PRIMITIVES["trim"] = function (s) { return s ? String(s).trim() : ""; };
+  PRIMITIVES["starts-with?"] = function (s, pfx) { return s ? String(s).indexOf(pfx) === 0 : false; };
+  PRIMITIVES["ends-with?"] = function (s, sfx) { var str = String(s || ""); return str.indexOf(sfx, str.length - sfx.length) !== -1; };
+  PRIMITIVES["escape"] = function (s) {
+    if (!s) return "";
+    return String(s).replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;").replace(/"/g, "&quot;");
+  };
+  PRIMITIVES["strip-tags"] = function (s) { return s ? String(s).replace(/<[^>]*>/g, "") : ""; };
+  PRIMITIVES["split"] = function (s, sep) { return s ? String(s).split(sep) : []; };
+  PRIMITIVES["join"] = function (lst, sep) { return (lst || []).join(sep !== undefined ? sep : ""); };
+  PRIMITIVES["pluralize"] = function (n, singular, plural) { return n === 1 ? singular : (plural || singular + "s"); };
+
+  // Numeric
+  PRIMITIVES["clamp"] = function (val, lo, hi) { return Math.max(lo, Math.min(hi, val)); };
+  PRIMITIVES["parse-int"] = function (s, def) { var n = parseInt(s, 10); return isNaN(n) ? (def !== undefined ? def : 0) : n; };
+  PRIMITIVES["format-decimal"] = function (n, places) { return Number(n || 0).toFixed(places !== undefined ? places : 2); };
+
+  // Date formatting (basic)
+  PRIMITIVES["format-date"] = function (s, fmt) {
+    if (!s) return "";
+    try {
+      var d = new Date(s);
+      if (isNaN(d.getTime())) return String(s);
+      // Basic strftime-like: %Y %m %d %H %M %B %b %-d
+      var months = ["January","February","March","April","May","June","July","August","September","October","November","December"];
+      var short_months = ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"];
+      return fmt.replace(/%-d/g, d.getDate()).replace(/%d/g, ("0"+d.getDate()).slice(-2))
+        .replace(/%B/g, months[d.getMonth()]).replace(/%b/g, short_months[d.getMonth()])
+        .replace(/%Y/g, d.getFullYear()).replace(/%m/g, ("0"+(d.getMonth()+1)).slice(-2))
+        .replace(/%H/g, ("0"+d.getHours()).slice(-2)).replace(/%M/g, ("0"+d.getMinutes()).slice(-2));
+    } catch (e) { return String(s); }
+  };
+  PRIMITIVES["parse-datetime"] = function (s) { return s ? String(s) : NIL; };
+  PRIMITIVES["split-ids"] = function (s) {
+    if (!s) return [];
+    return String(s).split(",").map(function(x) { return x.trim(); }).filter(function(x) { return x; });
+  };
 
   // --- Evaluator ---