Restore CI and release workflows

[yvette-carlisle]

Summary

• restore GitHub Actions for language checks, Pages deploy, and releases
• restore Dependabot for Cargo, GitHub Actions, and the remaining site npm workspace
• document that Radar/upstream refresh work stays in Codex App automations instead of GitHub Actions

Validation

• cargo make fmt-rust-check
• cargo make fmt-toml-check
• cargo make check-rust
• cargo make lint-rust
• cargo make test-rust
• cargo run -p decodex --bin decodex -- docs check
• cargo make build-node
• cargo make check-node
• actionlint
• ruby YAML parse for .github workflows and dependabot config