permissions: Allow fullscreen video requests on macOS

[shubham-padia]

On macOS, videos embedded in Zulip Desktop could not enter fullscreen mode because the app's permission handler did not explicitly grant fullscreen permissions.

This commit updates the ipcRenderer.on("permission-request") handler to include fullscreen, in addition to existing permissions such as notifications. With this change, video players (e.g., YouTube and Zulip-embedded media) can properly request fullscreen.

Tested on macOS to confirm fullscreen now works, and on Windows/Linux to ensure no regressions.

Fixes #1409.

Supersedes #1456

Screenshots and screen captures:

Platforms this PR was tested on:

• Windows
• macOS
• Linux (specify distro)

Self-review checklist

• Self-reviewed the changes for clarity and maintainability
  (variable names, code reuse, readability, etc.).

Communicate decisions, questions, and potential concerns.

• Explains differences from previous plans (e.g., issue description).
• Highlights technical choices and bugs encountered.
• Calls out remaining decisions and concerns.
• Automated tests verify logic where appropriate.

Individual commits are ready for review (see commit discipline).

• Each commit is a coherent idea.
• Commit message(s) explain reasoning and motivation for changes.

Completed manual review and testing of the following:

• Visual appearance of the changes.
• Responsiveness and internationalization.
• Strings and tooltips.
• End-to-end functionality of buttons, interactions and flows.
• Corner cases, error conditions, and easily imagined bugs.

[alya]

@andersk Are you up for reviewing this one?

[andersk]

This does not work with YouTube videos (Denied permissions request for fullscreen from https://www.youtube.com).

On Linux (both Xorg and Wayland), it does allow uploaded videos to be full-screened, but when you do this, the application menu bar disappears. This is almost certainly an upstream Electron bug that needs to be investigated.