Adds a new "Experimental" settings screen, accessible from the main settings page. This screen is now hidden from the bottom navigation bar.

Refines the full player's loading placeholder UI:
- Replaces the generic music note icon with the app's monochrome logo.
- Updates placeholder shapes from sharp corners to rounded ones for a softer look.
- Adjusts spacing, padding, and dimensions of placeholder elements for better visual balance and alignment with the final UI.
- Changes the placeholder color derivation for improved theme consistency.

Updates icons in the "Experimental" settings screen for better clarity:
- `Delay album carousel`: `MusicNote` -> `ViewCarousel`
- `Delay song title`: `Visibility` -> `LinearScale`
- `Delay progress bar`: `PlayCircle` -> `Outlined.LinearScale`
- `Show full player placeholders`: `Visibility` -> `Rectangle`

…ng-tweaks-option

Codex/add experimental loading tweaks option

Polishes the loading placeholder in the full player and refactors the `FileExplorerBottomSheet` to use a standard `CenterAlignedTopAppBar`.

**`FullPlayerContent.kt`:**
- Adjusts spacing, sizing, and corner radius of various placeholder elements for a more refined look.
- Modifies the placeholder icon's tint color and removes the alpha from the background surface.
- Increases the minimum height and spacing in the metadata and controls sections.

**`FileExplorerBottomSheet.kt`:**
- Replaces the custom header `Row` with a standard `CenterAlignedTopAppBar`.
- This change centralizes the title and moves the close and refresh buttons into the standard `navigationIcon` and `actions` slots.

**Other Changes:**
- **`SettingsScreen.kt`**: Updates the "Experimental" settings icon from a warning symbol to a science beaker.
- **`ExperimentalSettingsScreen.kt`**: Reduces padding and spacing for a more compact layout.

…or-placeholders

Align full player placeholder spacing