Add filter menu support to home page for V2EX content categories

[Copilot]

Implemented a comprehensive filter menu system for the V2EX home page, allowing users to browse content by different categories including 技术, 创意, 好玩, Apple, 酷工作, and more.

Changes Made

Core State Management

• Added selectedTab property to FeedState to track the current filter selection
• Enhanced FeedActions.FetchData.Start to accept a tab parameter for category-specific data fetching
• Introduced new FeedActions.ChangeTab action for seamless tab switching
• Updated feedStateReducer to handle tab changes with automatic content refresh

UI Implementation

• Created FeedTabFilter component with horizontal scrollable tab picker
• Integrated filter UI into FeedPage positioned above the feed content
• Applied consistent styling with visual highlighting for selected tabs
• Maintains responsive design principles with proper spacing and typography

Bug Fix

• Fixed Tab.displayName() method in TabInfo.swift which was incorrectly returning empty strings instead of localized category names

User Experience

The filter menu provides 10 content categories (全部, 技术, 创意, 好玩, Apple, 酷工作, 交易, 城市, 问与答, 最热) with:

• Automatic content refresh when switching between categories
• Visual feedback with blue highlighting for the selected tab
• Smooth horizontal scrolling for easy navigation
• Persistent filter state during app usage

The implementation follows the existing Redux-like architecture pattern and integrates seamlessly with current V2EX API endpoints, ensuring consistent performance and maintainability.

Fixes #3.

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