Change GitHub Actions runner to self-hosted

Switch from GitHub-hosted macOS-15 runners to self-hosted runners for:
- Better performance with local caching
- More control over the build environment
- Reduced GitHub Actions usage costs
- Faster build times with pre-configured environment

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   test:
-    runs-on: macos-15
+    runs-on: self-hosted
     
     strategy:
       matrix:
@@ -68,7 +68,7 @@ jobs:
         fail_ci_if_error: false
 
   build-swift:
-    runs-on: macos-15
+    runs-on: self-hosted
     timeout-minutes: 30
     
     env: