CI: standardize Actions (paths + concurrency + runners)

[0xLeif]

Standardizes the push/PR CI workflow to the CorvidLabs CI standard.

Changes (ci.yml)

• Add a paths: filter for the single-crate Rust layout: src/**, Cargo.toml, Cargo.lock, .github/workflows/ci.yml. Doc/README/LICENSE-only edits no longer trigger the 3-OS build matrix + clippy.
• Add a concurrency: group (ci-${{ github.ref }}) with cancel-in-progress: true so superseded runs are cancelled.
• Bump actions/checkout@v4 -> @v5.
• Add timeout-minutes to each job (check: 30, lint: 20).
• Runners unchanged: GitHub-hosted only (PUBLIC repo) — ubuntu/macos/windows-latest matrix for check, ubuntu-latest for lint.

Unchanged (already compliant)

• pages.yml: already scoped to docs/** with concurrency + ubuntu-latest.
• release.yml: tag-push only (v*) — no paths: per standard; GitHub-hosted matrix is PUBLIC-compliant.

No fledge.toml present, so native cargo commands are used.

Mirrors the CorvidLabs/merlin CI standard.

[gemini-code-assist]

Note

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