feat: update README and card version to 1.6.1, enhance update tracking details

[RF1705]

Title: Show OCI image versions in container table

## Summary

This PR updates the Dockge Card to show optional OCI image versions when they are available from the Home Assistant integration.

If a container sensor provides:

```yaml
image_version: 2026.5.4

the card now displays that value in the container table. If no image_version is available, it falls back to the existing image_tag display.

Why

Many images use generic tags such as stable, latest, or main, while the actual application version is exposed through the OCI label:

org.opencontainers.image.version

With the matching Dockge API and ha-dockge integration changes, the card can now show the real app version instead of only the image tag.

Changes

• Prefer image_version over image_tag in the popup container table.
• Keep image_tag as fallback for images without OCI version labels.
• Bump card version to 1.6.1.
• Update README feature text.
• Update cache-busting example to v=1.6.1.

Behavior

Before:

Image: stable

After, when image_version exists:

Image: 2026.5.4

Fallback behavior remains unchanged:

Image: stable

Compatibility

This is backward-compatible with older ha-dockge versions.

If the sensor does not provide image_version, the card continues to display image_tag exactly as before.

Testing

Validated JavaScript syntax with:

node --check dockge-card.js