feat: screenshots page on all devices, share cleanup on Pixel only

[jawzf]

Description

The Screenshots page (Security and privacy) was limited to Google devices because "Delete shared screenshots" detects the Pixel screenshot preview. Auto-clean and the cleaned-so-far stats don't depend on that UI, so the page now shows on every device on Android 11+:

• The "After sharing" section only shows on Google devices, or when "Enable unsupported features" is on. Its two search entries are only indexed on Google devices, so search doesn't point at a hidden row.
• Auto-clean now scans DCIM/Screenshots/ as well as Pictures/Screenshots/. Pixel and AOSP save to the second, while Samsung, Xiaomi and most OnePlus/Oppo devices save to the first.

Type of change

• Bug fix
• New feature
• UI / visual update
• Performance improvement
• Refactoring / cleanup
• Translations
• Build / CI tooling

UI changes

No change on Pixel. On other devices the page shows only the Auto-clean and Cleaned so far sections.

Checklist

Before submitting, please make sure:

• The base branch is set to develop (not main).
• The app builds cleanly locally with ./gradlew assembleDebug.
• Unit tests pass with ./gradlew testDebugUnitTest.
• You tested the changes on a device or emulator (including Shizuku or Root if applicable).
• New preferences use SettingsRepository for keys and getter/setter methods.
• New user-facing settings are registered in FeatureRegistry.kt for search indexing.
• New UI follows the design system in ui/core/ (RoundedCardContainer, IconToggleItem, etc.).
• Strings are added to res/values/strings.xml and drawables use rounded variants (R.drawable.rounded_*).

Tested on a Pixel emulator: the page is unchanged, and a screenshot saved to DCIM/Screenshots/ gets the auto-clean notification. The hidden "After sharing" section on non-Google devices wasn't tested on a real device.

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