chore: Add UI linter back (#3230)

# What does this PR do?

1. Adds `scripts/run-ui-linter.sh`
- Light script that checks whether `node_modules`,`eslint`, and
`prettier` exist before running linter
- When I introduced [the linter for the
UI](https://github.com/llamastack/llama-stack/pull/3156/files#diff-63a9c44a44acf85fea213a857769990937107cf072831e1a26808cfde9d096b9)
it forced the UI linter on all users, the small `node_modules` check
means that only users that have installed the UI locally (since
`node_modules` is in the gitignore) will actually end up having this
run. Additionally this does not do any install and just runs the
existing linter/prettier as requested by @mattf
2. Updates `.github/workflows/pre-commit.yml` to run CI again
- When I introduced the UI linter in the CI [in this
PR](https://github.com/llamastack/llama-stack/pull/3191) a failure
occurred because dependabot needed to be updated to also bump the
`package-lock.json` which was done [in this
PR](https://github.com/llamastack/llama-stack/pull/3212). All of this to
say, we shouldn't observe failures from dependabot again.
3. Updates `.pre-commit-config.yaml`
    - Calls `scripts/run-ui-linter.sh`

## AI Assistance Notice
I used Copilot minimally. 

## Test Plan
As
[requested](https://github.com/llamastack/llama-stack/pull/3207#discussion_r2288004872)
by @mattf I ran this after removing all of my `node_modules` and the
linter passed.

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

scripts/run-ui-linter.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+set -e
+cd llama_stack/ui
+
+if [ ! -d node_modules ] || [ ! -x node_modules/.bin/prettier ] || [ ! -x node_modules/.bin/eslint ]; then
+  echo "UI dependencies not installed, skipping prettier/linter check"
+  exit 0
+fi
+
+npm run format
+npm run lint