feat: modernize Searchbar to Material Design 3

- Modernize the Searchbar to the latest specs: https://m3.material.io/components/search/
- Reuse newly introduced tokens (shape, motion, typography, color etc)
- Extract component specific tokens for easier maintenance.
- Get inspired from TextInput/TextField, Switch, Checkbox, FAB components which have gone through modernization.

# Current State

## Searchbar

**MD3 spec:** Search
**Specs link:** https://m3.material.io/components/search/specs

### Color tokens

- Container background: `surfaceContainerHigh` ✅
- Leading icon: `onSurfaceVariant` ✅
- Clear / trailing icons: `onSurfaceVariant` ✅
- Cursor: `primary` ✅
- [ ] Input text color: `onSurfaceVariant`; should be `onSurface`
- [ ] Placeholder text color: `onSurface`; should be `onSurfaceVariant` – these two are swapped ❌

### Spacing / sizing

- Bar height: `minHeight: 56` ✅
- Bar border radius: `7 * roundness` = 28dp (`corner.extra-large`) ✅ for baseline style
- View mode border radius: 0 (`corner.none`) ✅ for divided style
- Input font: `bodyLarge` (16sp, overrides `fontSize: 18` in `StyleSheet`) ✅

### Behavior

- Leading icon, clear icon, trailing icon, custom `right` render prop ✅
- `mode="bar"` maps to divided/baseline style with elevation ✅
- `mode="view"` maps to divided search view with bottom `Divider` ✅
- State layers on icons via `IconButton` + `TouchableRipple` ✅
- [ ] No focus animation: M3 Expressive (Feb 2025) requires the bar container margins to change from 24dp (unfocused) to 12dp (focused), creating a grow-wider effect; not implemented
- [ ] `mode` values (`"bar"` / `"view"`) do not align with M3 spec terminology (`"contained"` / `"divided (baseline)"`)
- [ ] M3 Expressive contained style is now the recommended style; the component partially implements the shape but missing the focus margin transition
- [ ] No results/suggestions container component: spec anatomy includes a “container for search suggestions or results” as element 6; consumers must build this themselves with no provided primitive

### Notes

- Should be moved to its own directory
- The `divided` style is deprecated in M3 Expressive in favor of `contained`; `mode="view"` implements the divided style
- Result grouping with gaps (M3 Expressive) is a consumer-level concern and does not need to be part of the component itself

Beginne damit, die Searchbar-Implementierung zu lokalisieren, und vergleiche ihre aktuellen Tokens, Farben, Größen und Modi mit den verlinkten Material 3 Search-Spezifikationen. Prüfe die Modernisierungsmuster in TextInput/TextField, Switch, Checkbox und FAB. Als abgeschlossen gilt die Aufgabe, wenn die Checkliste abgearbeitet, die komponentenspezifischen Tokens und die Verzeichnisstruktur aktualisiert sind und das Fokusverhalten sowie die Terminologie der ausgewählten Spezifikation entsprechen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.