refactor: extracted fetch mocking into reusable hookFetch utility

- Extracted fetch mocking logic into reusable `hookFetch()` utility function with middleware-style handler pattern.
- Replaced manual `globalThis.fetch` assignment and restoration across 10 test files with `hookFetch()` calls using `using` statement for automatic cleanup.
- Implemented Disposable pattern with Symbol.dispose for fetch hook resource management, eliminating try-finally blocks.
- Exported `hookFetch` from utils public API to enable consistent fetch mocking across packages.

.omp/rules/ts-hook-fetch.md

@@ -0,0 +1,37 @@
+---
+description: Use hookFetch instead of assigning globalThis.fetch directly in tests
+condition: "globalThis\\.fetch\\s*="
+scope: "tool:edit(**/*.test.{ts,tsx,js,jsx}), tool:write(**/*.test.{ts,tsx,js,jsx})"
+---
+
+**Do not assign `globalThis.fetch = ...` directly in tests.**
+
+## Why it's wrong
+
+- It bypasses the project's standard fetch mocking helper
+- It is easier to forget restoration and leak state across tests
+- It makes test mocking inconsistent across the codebase
+
+## What to use instead
+
+Use `hookFetch` from `@oh-my-pi/pi-utils`:
+
+```ts
+import { hookFetch } from "@oh-my-pi/pi-utils";
+
+using _hook = hookFetch((input, init, next) => {
+	// return a mocked Response, or delegate with next(input, init)
+});
+```
+
+## Examples
+
+```ts
+// WRONG
+globalThis.fetch = async () => new Response("ok");
+
+// RIGHT
+using _hook = hookFetch(() => new Response("ok"));
+```
+
+If you need to intercept fetch in tests, use `hookFetch`.