feat(javascript): report observed export property presence (#1160)

* feat(javascript): report observed export property presence

Extend compare_javascript_export_shapes so each retained return variant
lists observed property names and each change reports presence independently
of value resolution. Complete parent coverage classifies one-sided names as
added or removed even when static values stay unknown.

Fixes #725

* test(javascript): match unknown export-shape values by availability

Nested availability objects include a reason when values stay unresolved.
Assert availability through objectContaining so presence-only added and
removed rows still verify unknown values.

* fix(javascript): preserve uncertain export property presence and locations

* fix(javascript): normalize presence and preserve local property coverage

* fix(javascript): require present discriminants for return pairing

* fix(javascript): normalize retained shapes before comparison

* refactor(javascript): share return projection with executable examples

* fix(javascript): localize uncertainty for missing mutated slots

* fix(javascript): bind advertised export examples to exact artifacts

* fix(javascript): keep uncertain property flow as candidates

---------

Co-authored-by: morluto <76467478+morluto@users.noreply.github.com>

src/domain/javascript/javascriptExportShapeComparisonIdentity.ts

@@ -2,7 +2,12 @@ import { createHash } from "node:crypto";
 
 import canonicalize from "canonicalize";
 
-/** Canonically encode one export-shape comparison value. */
+/**
+ * Canonically encode one export-shape comparison value.
+ *
+ * Comparison identifiers hash the full result semantics, including each
+ * change's presence object and the per-variant property inventories.
+ */
 export const canonicalExportShapeValue = (value: unknown): string => {
   const encoded = canonicalize(value);
   if (encoded === undefined)