refactor: move mission flow state into game store

docs/technical/mission-flow.md

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+# Mission Flow
+
+This document describes the mission intro and mission 2 prototype flow after it was merged into the current architecture.
+
+## Source Of Truth
+
+Mission flow state lives in the global game store:
+
+```txt
+src/managers/stores/useGameStore.ts
+```
+
+The store owns the `missionFlow` slice:
+
+```ts
+missionFlow: {
+  step: GameStep;
+  activityCity: boolean;
+  playerName: string;
+  canMove: boolean;
+  dialogMessage: string | null;
+}
+```
+
+This keeps global gameplay state in Zustand instead of splitting it across a separate mission store or a gameplay manager.
+
+## Managers Boundary
+
+Managers stay responsible for local runtime services:
+
+- `AudioManager` owns audio elements, audio pools, music playback, category volume, and stereo pan.
+- `InteractionManager` owns transient focused/nearby/held interaction handles.
+
+Mission progression is not owned by a manager. Components update the store through explicit actions such as `setFlowStep`, `setCanMove`, `showDialog`, and `hideDialog`.
+
+## Runtime Components
+
+- `src/components/game/GameFlow.tsx` reacts to `missionFlow.step` and triggers one-off side effects such as intro audio and movement unlocks.
+- `src/components/zone/ZoneDetection.tsx` reads the camera position and moves the flow to a target step when the player enters a configured zone.
+- `src/components/three/interaction/CentralObject.tsx` and `VillageoisHelperObject.tsx` expose temporary interactive mission objects.
+- `src/pages/page.tsx` mounts mission HTML overlays: `IntroUI`, `BienvenueDisplay`, and `DialogMessage`.
+- `src/world/player/PlayerController.tsx` reads `missionFlow.canMove` as an additional movement lock.
+
+## Step Sequence
+
+The prototype currently uses these steps:
+
+```ts
+"intro" |
+  "start-intro" |
+  "naming" |
+  "bienvenue" |
+  "star-move" |
+  "mission2" |
+  "searching" |
+  "helped" |
+  "manipulation" |
+  "outOfFabrik";
+```
+
+These steps are mission-flow prototype states. They do not replace `mainState` or the repair mission step machine used by `RepairGame`.
+
+## Zone Configuration
+
+Zone triggers live in:
+
+```txt
+src/data/zones.ts
+```
+
+Each zone has an id, position, radius, height, and `targetStep`. `ZoneDetection` marks a zone as triggered after the first activation so the same zone does not replay its transition every frame.
+
+## Rules
+
+- Keep mission flow state in `useGameStore.missionFlow`.
+- Do not reintroduce `GameStepManager` for global state transitions.
+- Do not create a second Zustand store for mission flow unless the state becomes independent from game progression.
+- Keep side effects such as audio playback in components or service managers, but keep the state transition itself in the store.
+- Keep per-frame values such as camera position and zone distance checks out of Zustand.