Fix Apple Metal runtime archive extraction

[Cashie1597]

Summary

• handle Apple Metal runtime archives served as gzip tar despite the .zip suffix
• add HTTP/content diagnostics, archive validation, optional checksum lookup, and friendly runtime install errors
• display Apple Silicon shared memory as Unified Memory instead of VRAM 0.0 GB

Root cause

The Apple Metal runtime URL returns HTTP 200 with Content-Type: application/gzip and gzip bytes, not a ZIP file. The installer assumed ZIP and surfaced the ZIP parser EOCD error to users.

Verification

• cargo check
• cargo test
• cargo test live_downloads_apple_metal_runtime -- --ignored --nocapture
• npm run build

Note: npm test -- --run still fails because this repo currently runs WDIO e2e specs under Vitest without a browser context, plus an existing formatBytes expectation mismatch. Not part of this runtime fix.