CI: standardize Actions (paths + concurrency + runners)

[0xLeif]

Standardizes GitHub Actions for this PUBLIC shell-based fledge plugin (bin/* scripts; no Package.swift/Cargo/package.json/lockfile/fledge.toml).

• ci.yml: add paths: [bin/**, .github/workflows/ci.yml] to push & pull_request so README/docs-only changes no longer trigger shellcheck+smoke CI.
• ci.yml: add concurrency: ci-${{ github.ref }} with cancel-in-progress: true.
• ci.yml: bump actions/checkout@v4 → @v5; add timeout-minutes: 10 to both jobs.
• ci.yml: runners left on ubuntu-latest (correct for a PUBLIC repo — GitHub-hosted only).
• pages.yml: already site-scoped + concurrency + correct runner; appended .github/workflows/pages.yml to its paths set, bumped checkout → @v5, added timeout-minutes: 10. Existing step logic preserved.

Mirrors the CorvidLabs/merlin CI standard.

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.