chore: upgrade GitHub Actions to Node.js 24 compatible versions

[MantisClone]

Problem

Deploy and PR validation workflows use GitHub Actions running on deprecated Node.js 20. These will be forced to Node.js 24 starting June 2, 2026.

Proposed Solution

• actions/checkout@v3/@v5 → @v6
• actions/setup-node@v3 → @v6
• peaceiris/actions-gh-pages@v3 → @v4 (latest)
• node-version 18 → 22

Considerations

• Both deploy.yml and pr.yml updated
• All actions bumped to latest available major versions

Closes #30

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

Upgrades all GitHub Actions in deploy.yml and pr.yml to their latest major versions (actions/checkout@v6, actions/setup-node@v6, peaceiris/actions-gh-pages@v4) and bumps the CI Node.js version from 18 to 22, ahead of the June 2026 Node.js 24 enforcement deadline.

• actions/checkout: v5/v3 → v6 (both workflows)
• actions/setup-node: v3 → v6 (both workflows)
• peaceiris/actions-gh-pages: v3 → v4 (deploy workflow)
• node-version: 18 → 22 (both workflows)
• No compatibility issues: lockfileVersion: 3 works with Node 22's npm, no engines or .nvmrc constraints exist, and all project dependencies support Node 22

Confidence Score: 5/5

• This PR is safe to merge — it only bumps CI action versions and Node.js version with no functional code changes.
• All changes are version bumps in CI workflow files only. Every target version has been verified to exist and be the latest major release. The Node.js upgrade from 18 to 22 is compatible with the project's lockfile (v3), dependencies, and has no conflicting engine constraints. No application code is changed.
• No files require special attention.

Important Files Changed

Filename	Overview
.github/workflows/deploy.yml	Bumps actions/checkout from v5 to v6, actions/setup-node from v3 to v6, peaceiris/actions-gh-pages from v3 to v4, and node-version from 18 to 22. All versions are valid and latest majors.
.github/workflows/pr.yml	Bumps actions/checkout from v3 to v6, actions/setup-node from v3 to v6, and node-version from 18 to 22. All versions are valid and latest majors.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[PR Opened / Release Published] --> B{Workflow}
    B -->|pull_request| C[pr.yml]
    B -->|release published| D[deploy.yml]

    C --> C1["actions/checkout@v6"]
    C1 --> C2["actions/setup-node@v6\n(Node 22)"]
    C2 --> C3["npm ci"]
    C3 --> C4["npm test"]
    C4 --> C5["npm run validate"]

    D --> D1["actions/checkout@v6"]
    D1 --> D2["actions/setup-node@v6\n(Node 22)"]
    D2 --> D3["npm ci"]
    D3 --> D4["npm run validate"]
    D4 --> D5["Build dist/"]
    D5 --> D6["Preserve historical snapshot"]
    D6 --> D7["peaceiris/actions-gh-pages@v4\nDeploy to GH Pages"]

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_{Last reviewed commit: d2961ed}