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>

hosts/python/tests/run_tests.py

@@ -273,7 +273,7 @@ for expr in parse_all(framework_src):
 args = [a for a in sys.argv[1:] if not a.startswith("--")]
 
 # Tests requiring optional modules (only with --full)
-REQUIRES_FULL = {"test-continuations.sx", "test-continuations-advanced.sx", "test-types.sx", "test-freeze.sx", "test-strict.sx", "test-cek.sx"}
+REQUIRES_FULL = {"test-continuations.sx", "test-continuations-advanced.sx", "test-types.sx", "test-freeze.sx", "test-strict.sx", "test-cek.sx", "test-cek-advanced.sx", "test-signals-advanced.sx"}
 
 test_files = []
 if args: