[17.0][IMP] voip_oca: Update z-index for proper layering

[carlos-lopez-tecnativa]

When the web_responsive module is installed, the VoIP component is not displayed in the main menu because web_responsive has a higher z-index.

Before

https://github.com/user-attachments/assets/cbbedd60-b6e8-4be2-869a-e84047439386

After this commit, the VoIP component will always be displayed.

https://github.com/user-attachments/assets/f1ba597d-5e7e-4edc-8da8-e69eda84db7b

@Tecnativa @pedrobaeza @etobella could you please review this?

[OCA-git-bot]

Hi @etobella, some modules you are maintaining are being modified, check this out!

[pedrobaeza]

At the same time you are there, can you please hide the systray icon when no voip provider is set in the user?

[github-actions[bot]]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days. If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.

[etobella]

Could you try to show what happens if we open a readonly O2M line or opening a wizard?