Phase 7a: affinity annotations + fix parser escape sequences

Add :affinity :client/:server/:auto annotations to defcomp, with
render-target function combining affinity + IO analysis. Includes
spec (eval.sx, deps.sx), tests, Python evaluator, and demo page.

Fix critical bug: Python SX parser _ESCAPE_MAP was missing \r and \0,
causing bootstrapped JS parser to treat 'r' as whitespace — breaking
all client-side SX parsing. Also add \0 to JS string emitter and
fix serializer round-tripping for \r and \0.

Reserved word escaping: bootstrappers now auto-append _ to identifiers
colliding with JS/Python reserved words (e.g. default → default_,
final → final_), so the spec never needs to avoid host language keywords.

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

shared/sx/tests/run.py

@@ -184,6 +184,8 @@ env = {
     "dict-get": "_deferred",
     "append!": "_deferred",
     "inc": lambda n: n + 1,
+    # Component accessor for affinity (Phase 7)
+    "component-affinity": lambda c: getattr(c, 'affinity', 'auto'),
 }
 
 
@@ -286,6 +288,7 @@ def _load_deps_from_bootstrap(env):
             transitive_io_refs,
             compute_all_io_refs,
             component_pure_p,
+            render_target,
         )
         env["scan-refs"] = scan_refs
         env["scan-components-from-source"] = scan_components_from_source
@@ -298,6 +301,7 @@ def _load_deps_from_bootstrap(env):
         env["transitive-io-refs"] = transitive_io_refs
         env["compute-all-io-refs"] = compute_all_io_refs
         env["component-pure?"] = component_pure_p
+        env["render-target"] = render_target
         env["test-env"] = lambda: env
     except ImportError:
         eval_file("deps.sx", env)