feat: add "Content Warnings" toggle from tv version

[siriusvoid]

Summary

Adds a Content Warnings toggle from the TV version. The parental guide overlay had no
switch before, so it appeared at the start of every episode with no way to turn it off.
Now it's optional, and it stays on by default.

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

The overlay shows every time an episode starts and can't be turned off. For users who
already know a show's content ratings, seeing it on every play is unnecessary, so this
gives them a setting to switch it off.

Issue or approval

Fixes #1168

UI / behavior impact

• No UI change
• No behavior change
• UI changed only to fix a documented glitch/bug
• Behavior changed only to fix a documented bug/regression
• UI change has explicit maintainer approval
• Behavior change has explicit maintainer approval

Policy check

• I have read and understood CONTRIBUTING.md.
• This PR is small, focused, and limited to one problem.
• 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.
• 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.

Testing

• Tested on iOS emulator via Xcode and on my Android phone with a debug build
• Parental Guide toggle off -> overlay no longer shown on playback start
• Parental Guide toggle on -> overlay appears as before

Screenshots / Video

Breaking changes

None

Linked issues

Fixes #1168