Add CI workflows for Example apps

[Kyle-Ye]

Summary

• Add composite action .github/actions/build-example for reusable Xcode + Tuist + xcodebuild pipeline
• Add per-framework workflow files with platform matrix (iOS device, iOS Simulator, macOS)

Workflows

Workflow	Scheme	Runner	Xcode	Platforms
ag_example.yml	AGExample	macos-15	16.4	iOS, iOS Sim, macOS
rb_example.yml	RBExample	macos-15	16.4	iOS, iOS Sim, macOS
coreui_example.yml	CoreUIExample	macos-15	16.4	iOS, iOS Sim, macOS
bls_example.yml	BLSExample	macos-15	16.4	iOS, iOS Sim
gf_example.yml	GFExample	macos-26	26.3	iOS, iOS Sim, macOS
sfsymbols_example.yml	SFSymbolsExample	macos-15	16.4	iOS, iOS Sim, macOS

Test plan

• Verify workflow YAML syntax is valid
• Verify workflows trigger and build successfully on push