Phase 4: Eliminate nested CEK from HO form handlers

Higher-order forms (map, filter, reduce, some, every?, for-each,
map-indexed) now evaluate their arguments via CEK frames instead
of nested trampoline(eval-expr(...)) calls.

Added HoSetupFrame — staged evaluation of HO form arguments.
When all args are evaluated, ho-setup-dispatch sets up the
iteration frame. This keeps a single linear CEK continuation
chain instead of spawning nested CEK instances.

14 nested eval-expr calls eliminated (39 → 25 remaining).
The remaining 25 are in delegate functions (sf-letrec, sf-scope,
parse-keyword-args, qq-expand, etc.) called infrequently.

All tests unchanged: JS 747/747, Full 864/870, Python 679/679.

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

sx/sxc/pages/docs.sx

@@ -581,6 +581,8 @@
       "cek-reactive" (~plans/cek-reactive/plan-cek-reactive-content)
       "reactive-runtime" (~plans/reactive-runtime/plan-reactive-runtime-content)
       "rust-wasm-host" (~plans/rust-wasm-host/plan-rust-wasm-host-content)
+      "isolated-evaluator" (~plans/isolated-evaluator/plan-isolated-evaluator-content)
+      "mother-language" (~plans/mother-language/plan-mother-language-content)
       :else (~plans/index/plans-index-content))))
 
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