feat(pferde-feature): introduce Pferde management module with screens, ViewModel, and domain models

- Added `pferde-feature` module for managing horses, including list, detail, and editing views.
- Implemented `MsMasterDetailLayout` for PferdeScreen, integrating `MsDataTable`, `MsFilterBar`, and `MsActionToolbar`.
- Defined domain models (`Pferd`, `Geschlecht`, `PferdeStatus`) with mock data support.
- Updated roadmap to mark `Pferde-Verwaltung (MVP)` as complete.
- Registered the new module in `settings.gradle.kts` and `meldestelle-desktop` build configuration.
- Added previews for Pferde and Reiter components to support IDE render.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

frontend/shells/meldestelle-desktop/build.gradle.kts

@@ -35,6 +35,8 @@ kotlin {
       implementation(projects.frontend.features.veranstaltungFeature)
       implementation(projects.frontend.features.turnierFeature)
       implementation(project(":frontend:features:profile-feature"))
+      implementation(project(":frontend:features:reiter-feature"))
+      implementation(project(":frontend:features:pferde-feature"))
       implementation(project(":frontend:features:billing-feature"))
 
       // Compose Desktop