fix(e2e): docs_site test intermittently times out #1763

Description

The create docs_site e2e test (e2e/test/commands/create/docs_site/docs_site_test.dart) intermittently times out on main.

Failing run: https://github.com/VeryGoodOpenSource/very_good_cli/actions/runs/37757567540/job/113245773965

TimeoutException after 0:02:00.000000: Test timed out after 2 minutes.
FileSystemException: Deletion failed, path = '/tmp/MCMMJN' (OS Error: Directory not empty, errno = 39)

The failing commit (#1756) is unrelated to docs_site, and the following run on main (37779724241) passed on the same code, so this is flakiness, not a regression.

Root cause

The test has a 2-minute timeout, but it normally takes almost that long:

Most of the time goes to npm install. The generated project has no package-lock.json, and CI has no npm cache, so every run installs ~1,300 packages fresh from the registry. Timing each step locally:

On CI the time depends on registry speed, so the test sometimes runs past the limit.

The Directory not empty error is a side effect: the test teardown deletes the temp directory while npm is still writing to it after the timeout.

The 2-minute timeout was copied from the Dart/Flutter e2e tests. The other tests that install heavy dependencies already use longer limits: flame_game has 5 minutes and flutter_plugin has 8.

Proposed fix

1. Raise the timeout in docs_site_test.dart to Duration(minutes: 5), matching flame_game.
2. Optionally, speed up the install with npm install --no-audit --no-fund --prefer-offline. Caching npm through actions/setup-node won't work as-is, because it needs a lockfile and the template doesn't ship one.