ci: move actions to v5 for the node24 runtime

[viny4]

actions/checkout@v4 and setup-node@v4 run on node20, which GitHub is retiring; runners already force them onto node24 and warn. v5 is the first release that targets node24 natively.

Staying on v5 rather than the latest v7 because v5 is the smallest change that clears the warning, and the newer majors alter defaults this workflow does not need.

What does this change?

Why?

How was it tested?

Checklist

• npm test passes
• No new runtime dependencies (Electron is the only one)
• No innerHTML used with user-controlled data
• Security model unchanged (contextIsolation on, nodeIntegration off)
• No telemetry, analytics, or third-party requests added
• Logic with real rules in it lives in lib/ with tests