Migrate Files Settings screen to Jetpack Compose

[clementiano9]

Description

• Migrates CloudSettingsFragment (the Files Settings screen) to Jetpack Compose, adding CloudSettingsPage and deleting fragment_cloud_settings.xml
• Follows the pattern already used by HeadphoneControlsSettingsFragment, reusing the shared SettingSection / SettingRow / SettingRowToggle / Banner components
• Reworks CloudSettingsViewModel to expose a single StateFlow<UiState> instead of a LiveData sign-in state plus direct settings.*.value reads in the fragment. This also fixes a latent issue: the old screen read each switch value once at bind time, so a preference changed elsewhere (e.g.by sync) while the screen was open would not be reflected
• Adds CloudSettingsViewModelTest

Fixes # 753

Testing Instructions

1. Sign out (or use a free account) so the Plus rows render locked
2. Go to Profile → Files → ⋮ → Files settings
3. Toggle Auto Add To Up Next and Delete local file; reopen the screen and confirm the values persisted
4. Confirm Delete cloud file is hidden (not merely disabled) while not Plus
5. Tap any of the three locked Plus rows, the upgrade screen should open
6. Tap Learn More in the banner, the upgrade screen should open
7. Dismiss the banner with ✕; reopen the screen and confirm it stays dismissed
8. Sign in as Plus/Patron and confirm all six toggles are enabled, Delete cloud file appears, and the banner is gone
9. Confirm the analytics still fire: settings_files_shown on open, and the per-toggle events on each change

Screenshots

Checklist

• If this is a user-facing change, I have added an entry in CHANGELOG.md
• Ensure the linter passes (./gradlew spotlessApply to automatically apply formatting/linting)
• I have considered whether it makes sense to add tests for my changes
• All strings that need to be localized are in modules/services/localization/src/main/res/values/strings.xml
• Any jetpack compose components I added or changed are covered by compose previews
• I have updated (or requested that someone edit) [the Event Horizon schema](https://github.com/
  Automattic/EventHorizonSchemas/blob/trunk/schema/pocket-casts.yml) to reflect any new or changed analytics.

I have tested any UI changes...

• with different themes
• with a landscape orientation
• with the device set to have a large display and font size
• for accessibility with TalkBack

[CLAassistant]

All committers have signed the CLA.