fix(runtime-fallback): prefer numeric status codes over non-numeric in extraction chain

The nullish-coalescing chain could stop at a non-numeric value (e.g.
status: "error"), preventing deeper nested numeric statusCode values
from being reached. Switch to Array.find() with a type guard to always
select the first numeric value.

Adds 11 tests for extractStatusCode covering: top-level, nested
(data/error/cause), non-numeric skip, fallback to regex, and
precedence.

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

src/hooks/runtime-fallback/error-classifier.ts

@@ -33,8 +33,15 @@ export function extractStatusCode(error: unknown, retryOnErrors?: number[]): num
 
   const errorObj = error as Record<string, unknown>
 
-  const statusCode = errorObj.statusCode ?? errorObj.status ?? (errorObj.data as Record<string, unknown>)?.statusCode ?? (errorObj.error as Record<string, unknown>)?.statusCode ?? (errorObj.cause as Record<string, unknown>)?.statusCode
-  if (typeof statusCode === "number") {
+  const statusCode = [
+    errorObj.statusCode,
+    errorObj.status,
+    (errorObj.data as Record<string, unknown>)?.statusCode,
+    (errorObj.error as Record<string, unknown>)?.statusCode,
+    (errorObj.cause as Record<string, unknown>)?.statusCode,
+  ].find((code): code is number => typeof code === "number")
+
+  if (statusCode !== undefined) {
     return statusCode
   }