fix: code-point string collation in LSM SSTable, COW trees/refs, sorted queries

Replaces localeCompare / raw relational operators with compareCodePoints (UTF-8
byte order) in the remaining persisted or native-facing comparison sites:
- SSTable sourceId sort + zone-map range check + binary search (graph LSM)
- COW TreeObject + RefManager name sorts (reproducible content hashes and ref
  listings across environments)
- getSortedIdsForFilter (numeric-aware; code-point for strings) so the JS sort
  fallback matches the native column store exactly

Deterministic across OS/Node/ICU and byte-identical to the native engine. No
migration: COW serialize/deserialize preserve stored order, so existing trees
keep their hashes; only new writes adopt code-point order.

src/storage/cow/RefManager.ts

@@ -20,6 +20,7 @@
  */
 
 import type { COWStorageAdapter } from './BlobStorage.js'
+import { compareCodePoints } from '../../utils/collation.js'
 
 /**
  * Reference type
@@ -226,7 +227,7 @@ export class RefManager {
     // Mark cache as valid
     this.cacheValid = true
 
-    return refs.sort((a, b) => a.name.localeCompare(b.name))
+    return refs.sort((a, b) => compareCodePoints(a.name, b.name))
   }
 
   /**

src/storage/cow/TreeObject.ts

@@ -15,6 +15,7 @@
  */
 
 import { BlobStorage } from './BlobStorage.js'
+import { compareCodePoints } from '../../utils/collation.js'
 
 /**
  * Tree entry: name → blob hash mapping
@@ -98,7 +99,12 @@ export class TreeBuilder {
    */
   async build(): Promise<string> {
     const tree: TreeObject = {
-      entries: this.entries.sort((a, b) => a.name.localeCompare(b.name)),
+      // Code-point (UTF-8 byte) order so the serialized tree — and therefore its
+      // content hash — is reproducible across environments (localeCompare's default
+      // locale varies by OS/Node/ICU). Sorting happens only here at write time;
+      // deserialize() preserves stored order, so existing trees keep their hashes
+      // and stay valid — no migration needed.
+      entries: this.entries.sort((a, b) => compareCodePoints(a.name, b.name)),
       createdAt: Date.now()
     }