ci(workflows): upgrade GitHub Actions to native Node 24 runtimes (Phase 18)

[k2kirov]

Upgrade GitHub Actions to Native Node 24 Runtimes (Phase 18)

Addresses the runner deprecation annotation:

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4, pnpm/action-setup@v3.

1. Upgraded Actions across all 5 Workflows:

   • actions/checkout: @v4 $\rightarrow$ @v7
   • actions/setup-node: @v4 $\rightarrow$ @v7
   • pnpm/action-setup: @v3 $\rightarrow$ @v6
   • actions/upload-artifact: @v4 $\rightarrow$ @v7
   • actions/configure-pages: @v5 $\rightarrow$ @v6
   • actions/upload-pages-artifact: @v3 $\rightarrow$ @v5
   • actions/deploy-pages: @v4 $\rightarrow$ @v5
   • changesets/action: @v1 $\rightarrow$ @v2

2. Benefits:

   • Completely eliminates deprecation warnings and runner forced runtime overrides.
   • Future-proofs CI/CD ahead of the September 16, 2026 removal of the Node 20 runtime on GitHub-hosted runners.