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/model-discovery.test.ts

@@ -8,7 +8,7 @@ import { writeModelCache } from "@oh-my-pi/pi-catalog/model-cache";
 import { kNoAuth, ModelRegistry } from "@oh-my-pi/pi-coding-agent/config/model-registry";
 import { resetSettingsForTest } from "@oh-my-pi/pi-coding-agent/config/settings";
 import { AuthStorage } from "@oh-my-pi/pi-coding-agent/session/auth-storage";
-import { Snowflake } from "@oh-my-pi/pi-utils";
+import { removeSyncWithRetries, Snowflake } from "@oh-my-pi/pi-utils";
 
 describe("ModelRegistry runtime discovery", () => {
 	let tempDir: string;
@@ -56,7 +56,7 @@ describe("ModelRegistry runtime discovery", () => {
 		}
 		authStorage.close();
 		if (tempDir && fs.existsSync(tempDir)) {
-			fs.rmSync(tempDir, { recursive: true });
+			removeSyncWithRetries(tempDir);
 		}
 	});