fix(hnsw): entry point recovery prevents import failures and log spam

Fixes critical production bug where HNSW index operations would fail
and spam thousands of console.error messages during large imports.

Root cause: rebuild() nullifies entryPointId via clear(), and if
getHNSWSystem() returns null (missing/corrupted system data), the
entry point was never recovered from loaded nouns.

Changes:
- Add entry point recovery in rebuild() after loading nouns
- Add entry point recovery in search() for corrupted state
- Add entry point recovery in search() when entry point noun deleted
- Remove console.error spam in search() and addItem()
- Standardize 404 error detection in GCS/S3/Azure storage adapters

Tested: All entry point scenarios now recover gracefully without
log spam. Empty index returns empty results silently.

src/storage/adapters/s3CompatibleStorage.ts

@@ -3628,11 +3628,15 @@ export class S3CompatibleStorage extends BaseStorage {
       const bodyContents = await response.Body.transformToString()
       return JSON.parse(bodyContents)
     } catch (error: any) {
-      if (
+      // S3 may return not found errors in different formats
+      const isNotFound =
         error.name === 'NoSuchKey' ||
+        error.code === 'NoSuchKey' ||
+        error.$metadata?.httpStatusCode === 404 ||
         error.message?.includes('NoSuchKey') ||
-        error.message?.includes('not found')
-      ) {
+        error.message?.includes('not found') ||
+        error.message?.includes('404')
+      if (isNotFound) {
         return null
       }