Spec eval-cond and process-bindings in render.sx (remove platform implementations)

eval-cond and process-bindings were hand-written platform JS in
bootstrap_js.py rather than specced in .sx files. This violated the
SX host architecture principle. Now specced in render.sx as shared
render adapter helpers, bootstrapped to both JS and Python.

eval-cond handles both scheme-style ((test body) ...) and clojure-style
(test body test body ...) cond clauses. Returns unevaluated body
expression for the adapter to render in its own mode.

process-bindings evaluates let-binding pairs and returns extended env.

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

shared/sx/ref/bootstrap_py.py

@@ -236,6 +236,8 @@ class PyEmitter:
             "map-indexed": "map_indexed",
             "map-dict": "map_dict",
             "eval-cond": "eval_cond",
+            "eval-cond-scheme": "eval_cond_scheme",
+            "eval-cond-clojure": "eval_cond_clojure",
             "process-bindings": "process_bindings",
             # deps.sx
             "scan-refs": "scan_refs",