fix(kernel-utils): use Object.is for value equality in decomposeMetadata

=== fails for NaN (NaN !== NaN), so a NaN value shared by all germs was
never promoted to a constraint — it remained in each germ's distinguishing
metadata instead. Object.is correctly treats NaN === NaN and is consistent
with the type-tagged encoding already used in collapseEquivalent.

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

Author: grypez

packages/kernel-utils/src/sheaf/sheafify.ts

@@ -121,7 +121,7 @@ const decomposeMetadata = <MetaData extends Record<string, unknown>>(
     const val = first[key];
     const shared = stalk.every((entry) => {
       const meta = entry.metadata;
-      return key in meta && meta[key] === val;
+      return key in meta && Object.is(meta[key], val);
     });
     if (shared) {
       constraints[key] = val;