Add 125 new tests: CEK-advanced, signals, integration (1063/1063)

New test files:
- test-cek-advanced.sx (63): deep nesting, complex calls, macro
  interaction, environment stress, edge cases
- test-signals-advanced.sx (24): signal types, computed chains,
  effects, batch, swap patterns
- test-integration.sx (38): parse-eval roundtrip, render pipeline,
  macro-render, data-driven rendering, error recovery, complex patterns

Bugs found:
- -> (thread-first) doesn't work with HO special forms (map, filter)
  because they're dispatched by name, not as env values. Documented
  as known limitation — use nested calls instead of ->.
- batch returns nil, not thunk's return value
- upcase not a primitive (use upper)

Data-first HO forms attempted but reverted — the swap logic in
ho-setup-dispatch caused subtle paren/nesting issues. Needs more
careful implementation in a future session.

Co-Authored-By: Claude Opus 4.6 (1M context) <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 = "2026-03-15T15:31:20Z";
+  var SX_VERSION = "2026-03-15T16:12:31Z";
 
   function isNil(x) { return x === NIL || x === null || x === undefined; }
   function isSxTruthy(x) { return x !== false && !isNil(x); }