test: point native change-detection test at split workflows

[HermesYP]

Fixes the test failure exposed by #2.

Problem

tests/ci-native-change-detection.test.ts hardcodes a path to the workflow file that #2 deleted:

Error: ENOENT: no such file or directory, open '.../.github/workflows/ci.yml'
    at tests/ci-native-change-detection.test.ts:8:18

This surfaced as a Frontend check failure on #2 (the Test step: 101 tests, 1 fail). #2 was merged before that signal was acted on, so main currently has a failing frontend check — this PR restores it to green.

The coupling was invisible until the file was removed: the test reads the workflow as a text fixture and asserts on its contents, so deleting the workflow broke a test rather than a workflow.

Change

The test now reads the two split workflows instead of the one deleted file.

Assertion	Before	After
src-tauri and harbor-core are watched pathspecs	parsed ci.yml	parsed native-quality.yml
Both checks diff from the merge-base parent	counted 2 matches in ci.yml	counts 2 matches across frontend-quality.yml + native-quality.yml

Both assertions are preserved unchanged in intent; only their input files moved. The second test concatenates both workflows, so it still requires exactly two BASE_SHA="${GITHUB_SHA}^1" selections — it now genuinely verifies both workflows rather than one file containing both jobs.

Verification

The extraction regex is the subtle part, since the detection block contains a multi-line git diff continuation that does not end in \. I reproduced the test logic locally against the delivered workflow files:

extracted pathspecs: ["src-tauri","harbor-core"]
BASE_SHA pull_request selections: 2 (expected 2)
PASS  src-tauri watched
PASS  harbor-core watched
PASS  BASE_SHA selection count == 2

The Native check on this PR will self-skip as expected, because the change-detection step watches src-tauri, harbor-core, and native-quality.yml — not tests/.