重构应用程序架构，添加 OpenIM SDK 初始化和引导逻辑

docs/architecture.md

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+# Project Architecture
+
+This project uses Expo Router and follows a route-first + feature-module structure.
+
+## Directory Design
+
+- `app/`: Routing layer only (Expo Router pages and layouts).
+- `features/`: Business modules grouped by domain.
+- `providers/`: App-level providers and bootstrap orchestration.
+- `components/`: Reusable presentational components.
+- `hooks/`: Shared generic hooks (cross-feature).
+- `constants/`: Shared constants and theme tokens.
+
+## Current Module Split
+
+- `app/_layout.tsx`
+  - Root navigation composition only.
+  - Theme provider and route stack config.
+  - No SDK side effects.
+
+- `providers/app-bootstrap-provider.tsx`
+  - Central app bootstrap orchestration.
+  - Triggers feature bootstrap hooks.
+
+- `features/im/openim-bootstrap.ts`
+  - OpenIM SDK initialization and listener registration.
+  - One-time initialization guard.
+  - Local data directory creation and reuse.
+
+- `features/im/hooks/use-openim-bootstrap.ts`
+  - React lifecycle bridge for IM bootstrap.
+
+## Why This Structure
+
+- Keeps routing files focused on navigation.
+- Moves SDK side effects out of render paths.
+- Makes IM bootstrap testable and reusable.
+- Scales better when adding `features/chat`, `features/contact`, and `features/conversation`.
+
+## Next Suggested Refactors
+
+1. Move IM API wrappers into `features/im/services/`.
+2. Add `features/chat/hooks/use-chat-list.ts` and `features/chat/hooks/use-messages.ts`.
+3. Keep `app/(tabs)` as route shells and move business UI into `features/*/screens`.