refactor(Post, PostMapper, PostRepository, CreatePostScreen, HomeScreen): update communityId to channelId for improved clarity

- Renamed communityId to channelId across Post entity, PostMapper, and PostRepository for consistency and clarity.
- Updated CreatePostScreen to include channel selection functionality, enhancing user experience when creating posts.
- Adjusted HomeScreen to support filtering posts by channel, improving content organization.
- Refactored related interfaces and services to align with the new channelId terminology, ensuring a cohesive codebase.

app/(app)/(tabs)/_layout.tsx

@@ -9,7 +9,7 @@ import { useTotalUnreadCount } from '../../../src/stores';
 
 const TAB_BAR_HEIGHT = 56;
 const TAB_BAR_FLOATING_MARGIN = 12;
-const TAB_BAR_MARGIN = 24;
+const TAB_BAR_MARGIN = 20;
 
 export default function TabsLayout() {
   const { width } = useWindowDimensions();