Remove PROD_SHARE_DOMAIN constant and unify domain configuration

- Remove hard-coded PROD_SHARE_DOMAIN from src/constants/app.ts
- Update all sharing functionality to use environment-specific APP_SERVER
- Rewrite domain configuration documentation to reflect unified approach
- Simplify domain management with single APP_SERVER constant
- Update README.md examples to use APP_SERVER for all URL generation

This change eliminates the complexity of separate constants for different
URL types and provides consistent environment-specific configuration for
all functionality including sharing.

README.md

@@ -113,10 +113,11 @@ appearing in shared links during development.
 - ✅ **Type-Safe Configuration**: Full TypeScript support
 
 ### Quick Reference
+
 ```typescript
-// For sharing functionality (always production)
-import { PROD_SHARE_DOMAIN } from "@/constants/app";
-const shareLink = `${PROD_SHARE_DOMAIN}/deep-link/claim/123`;
+// For sharing functionality (environment-specific)
+import { APP_SERVER } from "@/constants/app";
+const shareLink = `${APP_SERVER}/deep-link/claim/123`;
 
 // For internal operations (environment-specific)
 import { APP_SERVER } from "@/constants/app";
@@ -124,6 +125,7 @@ const apiUrl = `${APP_SERVER}/api/claim/123`;
 ```
 
 ### Documentation
+
 - [Domain Configuration System](docs/domain-configuration.md) - Complete guide
 - [Constants and Configuration](src/constants/app.ts) - Core constants