fix: migrate coding-agent tests from fs.rm to removeWithRetries

Migrate 203 test files (356 call sites) from fs.rm/fs.rmSync to
removeWithRetries/removeSyncWithRetries to reduce EBUSY test failures
on Windows. removeWithRetries is now exported from @oh-my-pi/pi-utils.

The migration uses a regex-based approach that:
- Replaces fs.rm(path, { recursive, force }) → removeWithRetries(path)
- Replaces fs.rmSync(path, { recursive, force }) → removeSyncWithRetries(path)
- Replaces fs.rm(path) → removeWithRetries(path) (no options)
- Skips fs.rm/fs.rmSync inside template literals (bun --eval scripts)
- Adds imports to existing @oh-my-pi/pi-utils import or creates new one
- Removes unused fs imports where fs.rm was the only fs usage (4 files)

packages/coding-agent/test/git-reftable.test.ts

@@ -2,6 +2,7 @@ import { afterAll, beforeAll, describe, expect, test } from "bun:test";
 import * as fs from "node:fs/promises";
 import * as os from "node:os";
 import * as path from "node:path";
+import { removeWithRetries } from "@oh-my-pi/pi-utils";
 import { $ } from "bun";
 import * as git from "../src/utils/git";
 
@@ -55,9 +56,9 @@ describe.skipIf(!supportsReftable)("git reftable support", () => {
 
 	afterAll(async () => {
 		await $`git worktree remove ${worktreeDir} -f`.cwd(sharedRepoDir).quiet().nothrow();
-		await fs.rm(worktreeDir, { recursive: true, force: true }).catch(() => {});
-		await fs.rm(sharedRepoDir, { recursive: true, force: true }).catch(() => {});
-		await fs.rm(configRepoDir, { recursive: true, force: true }).catch(() => {});
+		await removeWithRetries(worktreeDir).catch(() => {});
+		await removeWithRetries(sharedRepoDir).catch(() => {});
+		await removeWithRetries(configRepoDir).catch(() => {});
 	});
 
 	test("resolves references in a reftable repository", async () => {