[Rigidity]

Adds a GitHub Actions workflow with four jobs:

• Test: cargo test --all-targets
• Clippy: cargo clippy --all-targets -- -D warnings
• Rust Format: cargo fmt --all --check
• Rue Format & Build: installs rue-cli at the version in Rue.toml, runs rue fmt --check, then rebuilds the puzzles with rue build -a -s -x -h and fails if anything under puzzles/ changes (including untracked files)

Also updates the README's Development section to reflect that CI now performs the compiled-puzzle check.

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Note

Low Risk
Adds CI and documentation only; no runtime, auth, or on-chain logic changes.

Overview
Adds a GitHub Actions CI workflow that runs on pushes to main and on pull requests, with concurrency cancellation per ref.

Four parallel jobs enforce quality gates: cargo test --all-targets, Clippy with warnings denied (also via RUSTFLAGS), cargo fmt --check, and a Rue job that pins rue-cli to the version in Rue.toml, runs rue fmt --check, rebuilds puzzles with rue build -a -s -x -h, and fails if puzzles/ is dirty afterward.

The README Development section is updated to state that CI already performs the compiled-puzzle freshness check (replacing the previous “CI should run…” wording).

^{Reviewed by Cursor Bugbot for commit 7495b4a. Bugbot is set up for automated code reviews on this repo. Configure here.}