ci: Use group key for self-hosted runner references (#286)

## Summary

- Switch all CI workflow `runs-on` values from bare strings to the
`group:` object syntax, which is required to properly target self-hosted
runner groups
- Remove `.claude/settings.json` (project-level Claude Code permissions
no longer needed)

## Test plan

- [ ] Verify CI workflows trigger and pick up the correct runner groups
- [ ] Confirm no regressions in test, release, and gh-page workflows

Assisted-by: Claude Opus 4.6 via Claude Code

Author: kejadlen

.claude/settings.json

@@ -8,7 +8,8 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on:
+      group: gusto-ubuntu-default
     steps:
       - uses: actions/checkout@v4
 
@@ -40,7 +41,8 @@ jobs:
 
     if: ${{ github.ref_type == 'tag' || github.ref == 'refs/heads/main' }}
     # Specify runner + deployment step
-    runs-on: ubuntu-latest
+    runs-on:
+      group: gusto-ubuntu-default
     steps:
       - name: Deploy to GitHub Pages
         id: deployment

.github/workflows/gh-page.yml

@@ -9,7 +9,8 @@ on:
 jobs:
   prepare-release:
     name: Prepare Release
-    runs-on: gusto-ubuntu-default
+    runs-on:
+      group: gusto-ubuntu-default
     outputs:
       version: ${{ steps.version.outputs.version }}
     steps:
@@ -63,7 +64,8 @@ jobs:
   build:
     name: Build ${{ matrix.target }}
     needs: prepare-release
-    runs-on: ${{ matrix.runner }}
+    runs-on:
+      group: ${{ matrix.runner }}
     strategy:
       fail-fast: false
       matrix:
@@ -122,7 +124,8 @@ jobs:
   release:
     name: Create GitHub Release
     needs: [prepare-release, build]
-    runs-on: gusto-ubuntu-default
+    runs-on:
+      group: gusto-ubuntu-default
     steps:
       - name: Download all artifacts
         uses: actions/download-artifact@v4

.github/workflows/release.yml

@@ -14,7 +14,8 @@ on:
 jobs:
   tests:
     name: Run Tests
-    runs-on: ubuntu-latest
+    runs-on:
+      group: gusto-ubuntu-default
     steps:
       - uses: actions/checkout@v4
       - run: rustup update