ci: add macos-latest to test matrix

Platform-specific code paths (Unix permission bits in `hook install`,
native clipboard via arboard, hook path resolution) are currently only
exercised on Ubuntu. Extend the `clippy` and `test` jobs to run on
`macos-latest` alongside `ubuntu-24.04` via a strategy matrix so these
paths get continuous coverage on macOS. `fmt`, `test-eval`, `msrv`,
`audit`, `dependency-review`, and `reuse` stay Ubuntu-only — they are
platform-agnostic and duplicating them would waste runner time. Windows
is intentionally out of scope for this ticket.

`fail-fast: false` keeps a failure on one OS from cancelling the other,
making regressions easier to diagnose.

Closes audit entry F-016 from #3.

Author: Sephyi

.github/workflows/ci.yml

@@ -36,9 +36,13 @@ jobs:
       - run: cargo fmt --check
 
   clippy:
-    name: Clippy
+    name: Clippy (${{ matrix.os }})
     needs: fmt
-    runs-on: ubuntu-24.04
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-24.04, macos-latest]
+    runs-on: ${{ matrix.os }}
     timeout-minutes: 15
     steps:
       - uses: actions/checkout@v4
@@ -50,9 +54,13 @@ jobs:
       - run: cargo clippy --all-targets -- -D warnings
 
   test:
-    name: Test
+    name: Test (${{ matrix.os }})
     needs: fmt
-    runs-on: ubuntu-24.04
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-24.04, macos-latest]
+    runs-on: ${{ matrix.os }}
     timeout-minutes: 15
     steps:
       - uses: actions/checkout@v4