Run CI on GitHub-hosted runners

[owjs3901]

Summary

• replace the self-hosted Linux runner with GitHub's ubuntu-latest runner
• remove comments specific to the private self-hosted runner pool

Verification

• bun install --frozen-lockfile
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace
• cargo doc --workspace --no-deps with RUSTDOCFLAGS=-D warnings
• bun run lint
• TypeScript checks for all frontend packages
• frontend static build
• release example-app build