Add F key shortcut to toggle player fullscreen

[tavyandy97]

Summary

Adds F as a shortcut to toggle fullscreen in the desktop player. Previously fullscreen was only reachable from the keyboard via F11 or, on macOS, Ctrl+Cmd+F.

PR type

• Reproducible bug fix
• UI glitch/bug fix
• Behavior bug/regression fix
• Small maintenance only, with no UI or behavior change
• Docs accuracy fix
• Translation/localization only
• Approved larger or directional change

Why

Plain F is the near-universal fullscreen binding across video players (YouTube, VLC, Plex, mpv). The player already handled F11 and Ctrl+Cmd+F, so users reaching for F got no response.

Desktop scope

Desktop only, all platforms (Windows, macOS, Linux). The change is confined to the desktop player's WebView controls UI at composeApp/src/desktopMain/resources/player-ui/controls.js. No shared/common code changed, and no Kotlin changed — it reuses the existing togglePlayerFullscreen() helper, which sends the same toggleFullscreen command the on-screen fullscreen button already sends.

Issue or approval

#445 — filed, but not yet approved. Opening this for maintainer consideration rather than claiming approval it doesn't have.

Flagging honestly: per CONTRIBUTING.md this is a behavior change (keyboard input / fullscreen) and needs an approved feature request first, so no PR type box below is truthful today and I've left them unticked rather than check a false one. The template check will fail on that. If #445 is approved, "Approved larger or directional change" applies and I'll update. If the change isn't wanted, happy to close this.

UI / behavior impact

• No UI change

This PR does change behavior (adds a keyboard binding), so none of the behavior boxes above can be ticked truthfully until #445 is approved.

Policy check

• I have read and understood CONTRIBUTING.md.
• This PR is small, focused, and limited to one problem.
• This PR is scoped to the desktop app, desktop packaging, desktop documentation, or shared code required for desktop behavior.
• This PR is not cosmetic-only.
• Any UI change fixes a linked glitch/bug and includes visual proof, or this PR has no UI change.
• Any behavior change fixes a linked bug/regression or has explicit approval, or this PR has no behavior change. — left unchecked deliberately: [Feature]: Bind F to toggle fullscreen in the desktop player #445 is not yet approved.
• This PR does not bundle unrelated refactors, cleanups, formatting, or drive-by changes.
• This PR does not add dependencies, architecture changes, migrations, or product-direction changes without explicit approval.
• I listed the testing performed below.

Scope boundaries

Intentionally not changed:

• The existing F11 and Ctrl+Cmd+F handling is untouched.
• The app-window fullscreen dispatcher in DesktopAppFullscreen.kt is untouched, so bare F does nothing outside the player.
• No other shortcuts added, and the unused actionShortcutCommandForEvent table (S/T/C/E/P) is left as-is rather than bundled in.
• No Kotlin, no new commands, no dependencies.

F is routed through the existing shortcutCommandForEvent table rather than the F11 branch, so it inherits the guards a letter key needs: modifier keys are rejected (Cmd+F, Ctrl+F, Alt+F fall through untouched), and dispatch happens after the activeModal || isTextEntryTarget check so typing "f" in a search field or with a modal open does not toggle fullscreen.

Testing

• node --check on controls.js passes.
• Traced the dispatch path by inspection: modifier guard at shortcutCommandForEvent, modal/text-entry guard ahead of dispatch, and noteChromeActivity() confirmed to no-op while chrome is hidden.

Not yet verified by running the app. Outstanding manual checks before this should be merged:

• F toggles into and out of fullscreen during playback
• Cmd+F / Ctrl+F do not toggle
• Typing "f" in the subtitle search field does not toggle
• F11 and Ctrl+Cmd+F still work

Screenshots / Video

Not a UI change.

Breaking changes

None.

Linked issues

#456

[tavyandy97]

@KhooLy When you get a chance, could you take a look?

If anything's missing or you'd like changes to the approach, let me know and I'll update it.

Thanks for your time!

[KhooLy]

Hi thanks for your PR but #594 is going to make much more besides this feature so If his PR gets merged this is stale, if his doesnt then I can merge this. Thanks for your time.