Add VisibilityService documentation and integration guide

- Create comprehensive documentation for the new VisibilityService, detailing its purpose, core concepts, and architecture.
- Include an integration guide for module developers, outlining best practices for registering services and handling app visibility changes.
- Add example code snippets for implementing visibility management in various service types, ensuring clarity and ease of use.
- Introduce a troubleshooting section to address common issues and provide debugging tips for developers.
- Enhance the VisibilityService integration guide with real-world examples to illustrate practical usage scenarios.

CLAUDE.md

@@ -80,6 +80,7 @@ const relayHub = injectService(SERVICE_TOKENS.RELAY_HUB)
 - `SERVICE_TOKENS.RELAY_HUB` - Centralized Nostr relay management
 - `SERVICE_TOKENS.NOSTR_CLIENT_HUB` - Nostr client services  
 - `SERVICE_TOKENS.AUTH_SERVICE` - Authentication services
+- `SERVICE_TOKENS.VISIBILITY_SERVICE` - App visibility and connection management
 
 **Core Stack:**
 - Vue 3 with Composition API (`<script setup>` style)
@@ -159,6 +160,16 @@ export const myModule: ModulePlugin = {
 - Base module provides core infrastructure services
 - Modules can register their own services in the DI container
 
+**⚠️ CRITICAL - WebSocket Connection Management:**
+- **ALWAYS integrate with VisibilityService for any module that uses WebSocket connections**
+- All services extending `BaseService` have automatic access to `this.visibilityService`
+- Register visibility callbacks during service initialization: `this.visibilityService.registerService(name, onResume, onPause)`
+- Implement proper connection recovery in `onResume()` handler (check health, reconnect if needed, restore subscriptions)
+- Implement battery-conscious pausing in `onPause()` handler (stop heartbeats, queue operations)
+- **Mobile browsers suspend WebSocket connections when app loses visibility** - visibility management is essential for reliable real-time features
+- See `docs/VisibilityService.md` and `docs/VisibilityService-Integration.md` for comprehensive integration guides
+- Future modules will likely ALL depend on WebSocket connections - plan for visibility management from the start
+
 ### **Centralized Infrastructure**
 
 **Nostr Relay Management:**