fix: tighten error detection to handle DOMException not extending Error

In some environments DOMException does not inherit from Error.
Use (error instanceof Error || error instanceof DOMException) for all
three detection functions to avoid missing IDB errors in those envs.

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

Author: leshniak

lib/storage/providers/IDBKeyValProvider/createStore.ts

@@ -10,7 +10,7 @@ const HEAL_ATTEMPTS_MAX = 3;
  * internal recovery (RepairDB -> delete -> recreate) also fails.
  */
 function isBackingStoreError(error: unknown): boolean {
-    return error instanceof Error && error.message.includes('Internal error opening backing store');
+    return (error instanceof Error || error instanceof DOMException) && (error as Error).message.includes('Internal error opening backing store');
 }
 
 /**
@@ -19,13 +19,13 @@ function isBackingStoreError(error: unknown): boolean {
  * WebKit bugs: https://bugs.webkit.org/show_bug.cgi?id=197050, https://bugs.webkit.org/show_bug.cgi?id=201483
  */
 function isConnectionLostError(error: unknown): boolean {
-    if (!(error instanceof Error)) return false;
-    const msg = error.message.toLowerCase();
+    if (!(error instanceof Error || error instanceof DOMException)) return false;
+    const msg = (error as Error).message.toLowerCase();
     return msg.includes('connection to indexed database server lost') || msg.includes('connection is closing');
 }
 
 function isInvalidStateError(error: unknown): boolean {
-    return error instanceof Error && error.name === 'InvalidStateError';
+    return (error instanceof Error || error instanceof DOMException) && (error as Error).name === 'InvalidStateError';
 }
 
 /** Errors that trigger a budgeted heal-and-retry in store(). */