feat(sasch40): add Nebenraum, Marktplatz minigame & trapdoor to Hinterzimmer

- Split GameBoy chassis brand header: 'AKT III' on clean dedicated second line
- Add 5-room tavern architecture: Schankraum, Nebenraum, Marktplatz, Hinterland, Hinterzimmer
- Introduce Nebenraum (Kemenate/Atelier) with Amy at her easel painting the neon banner and Zuluman magic mirror
- Update Marktplatz scene with Mario juggling chainsaws/hops and NAT on the festival stage
- Implement Wildschwein-Schnick-Schnack-Schnuck minigame against NAT (Best of 3, Keiler > Dickicht > Lanze > Keiler)
- Replace secret tap with cellar floor trapdoor ('Luke zum Hinterraum') initially invisible
- Update automated playtest covering all 25 screens with zero console/network errors
- Document all architectural decisions in projects/sasch40/AGENTS.md

projects/sasch40/frontend/src/components/GameBoyFrame.vue

@@ -45,7 +45,7 @@ function toggleInventory() {
       <div class="chassis-brand">
         <span class="brand-text">KÖNIG SASCHAS KRONKORKENKREUZZUG</span>
         <span v-if="store.currentAct !== 'intro'" class="brand-act">
-          {{ store.currentAct === 'prologue' ? '• AKT I' : store.currentAct === 'platformer' ? '• AKT II' : store.currentAct === 'tavern' ? '• AKT III' : store.currentAct === 'party_express' ? '• AKT IV' : store.currentAct === 'finale' ? '• AKT V' : '' }}
+          {{ store.currentAct === 'prologue' ? 'AKT I' : store.currentAct === 'platformer' ? 'AKT II' : store.currentAct === 'tavern' ? 'AKT III' : store.currentAct === 'party_express' ? 'AKT IV' : store.currentAct === 'finale' ? 'AKT V' : '' }}
         </span>
       </div>
       <button class="sound-toggle" @click="toggleAudio">
@@ -203,8 +203,10 @@ function toggleInventory() {
 
 .chassis-brand {
   display: flex;
+  flex-direction: column;
   align-items: center;
-  gap: 4px;
+  justify-content: center;
+  gap: 2px;
   overflow: hidden;
 }
 
@@ -218,7 +220,7 @@ function toggleInventory() {
 
 .brand-act {
   font-family: 'Press Start 2P', monospace;
-  font-size: 6px;
+  font-size: 5.5px;
   color: #f59e0b;
   white-space: nowrap;
 }