feat(validation): integrate ÖTO/FEI rule validations and centralized validators

- Added `OetoValidators` with live-validation for OEPS numbers, FEI-IDs, license classes, and horse data to align with ÖTO/FEI 2026 standards.
- Expanded `ReiterProfilViewModel` and `PferdProfilViewModel` to include validation states (`ValidationResult`) for enhanced form feedback and dirty state tracking.
- Standardized mock data in `Stores.kt` and `NennungModels.kt` to comply with updated validation rules.
- Created `OetoValidatorsTest` to ensure validation logic accuracy (30 unit tests, all green).
- Updated `build.gradle.kts` to include `kotlin.test` dependency for JVM testing.

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

frontend/shells/meldestelle-desktop/src/jvmMain/kotlin/at/mocode/desktop/v2/Stores.kt

@@ -98,7 +98,7 @@ object StoreV2 {
       geburtsdatum = "2001-01-01",
       besitzer = "Isabell Werth",
       lebensnummer = "DE 431316694401",
-      oepsNummer = "3H66"
+      oepsNummer = "3456601"  // OEPS-Format: 7 Ziffern (Validierungsregeln.md §1)
     ),
     Pferd(
       id = 2,
@@ -111,7 +111,7 @@ object StoreV2 {
       geburtsdatum = "2004-01-01",
       besitzer = "Madeleine Winter-Schulze",
       lebensnummer = "DE 443434443904",
-      oepsNummer = "2T15"
+      oepsNummer = "2345602"  // OEPS-Format: 7 Ziffern
     ),
     Pferd(
       id = 3,
@@ -124,7 +124,7 @@ object StoreV2 {
       geburtsdatum = "2002-01-01",
       besitzer = "Carl Hester & Roly Luard",
       lebensnummer = "NLD003NL0204840",
-      oepsNummer = "1V51"
+      oepsNummer = "1234603"  // OEPS-Format: 7 Ziffern
     ),
     Pferd(
       id = 4,
@@ -137,7 +137,7 @@ object StoreV2 {
       geburtsdatum = "2007-01-01",
       besitzer = "Beatrice Bürchler-Keller",
       lebensnummer = "DE 409090124007",
-      oepsNummer = "4U89"
+      oepsNummer = "4567604"  // OEPS-Format: 7 Ziffern
     ),
   )
 
@@ -146,10 +146,10 @@ object StoreV2 {
       id = 1,
       vorname = "Isabell",
       nachname = "Werth",
-      oepsNummer = "O-12345",
+      oepsNummer = "OEPS-1234567",  // OEPS-Format: Präfix + 7 Ziffern
       feiId = "10011469",
       verein = "RFV Graf von Schmettow Eversael",
-      lizenzKlasse = "RD4",
+      lizenzKlasse = "RD3",  // Höchste Dressur-Lizenz gemäß ÖTO (Validierungsregeln.md §3)
       startkartAktiv = true,
       startkartSaison = 2026,
       nation = "GER"
@@ -158,10 +158,10 @@ object StoreV2 {
       id = 2,
       vorname = "Jessica",
       nachname = "von Bredow-Werndl",
-      oepsNummer = "O-54321",
+      oepsNummer = "OEPS-2345678",
       feiId = "10019075",
       verein = "RFV Aubenhausen",
-      lizenzKlasse = "RD4",
+      lizenzKlasse = "RD3",
       startkartAktiv = true,
       startkartSaison = 2026,
       nation = "GER"
@@ -170,10 +170,10 @@ object StoreV2 {
       id = 3,
       vorname = "Charlotte",
       nachname = "Dujardin",
-      oepsNummer = "GB-9999",
+      oepsNummer = "OEPS-3456789",  // Hinweis: Internationale Reiter haben ggf. keine OEPS-Nr. — Platzhalter
       feiId = "10028445",
       verein = "Rowallan Activity Centre",
-      lizenzKlasse = "RD4",
+      lizenzKlasse = "RD3",
       startkartAktiv = true,
       startkartSaison = 2026,
       nation = "GBR"
@@ -182,10 +182,10 @@ object StoreV2 {
       id = 4,
       vorname = "Stefan",
       nachname = "Moser",
-      oepsNummer = "O-44332",
+      oepsNummer = "OEPS-4456789",
       feiId = "10011111",
       verein = "URFV Neumarkt/M.",
-      lizenzKlasse = "R2D2",
+      lizenzKlasse = "R2",  // Gültige Springen-Lizenz gemäß ÖTO (Validierungsregeln.md §3)
       startkartAktiv = true,
       startkartSaison = 2026,
       nation = "AUT",