feat(web): require GitHub auth before actions

[skulidropek]

Summary

• auto-load GitHub auth status when browser UI starts
• redirect to Auth and open GitHub OAuth prompt when no usable GitHub token is configured
• block create/menu actions until GitHub auth is loaded and usable

Verification

• bun run --cwd packages/app typecheck
• bun run --cwd packages/app lint
• bun run --cwd packages/app lint:tests
• bun run --cwd packages/app lint:effect
• bun run --cwd packages/app test
• bun run --cwd packages/app build:web
• curl -fsS http://127.0.0.1:4174/api/auth/github/status