Feature: Show a feed of posts from your groups (Implements #362)

[NotThatKindOfDrLiz]

Description

This PR implements a feature to show a feed of posts from all groups a user has joined, addressing issue #362.

Features Implemented

1. Created a new /feed route that shows posts from all groups the user is a member of
2. Added UI elements in the header for easy navigation to the feed
3. Implemented tabs for filtering between "Approved" and "All" posts
4. Created a specialized post display component that shows group context
5. Added appropriate loading states and empty state handling

Technical Details

• Efficient Data Fetching: Fetches posts group by group to avoid overwhelming relays
• Comprehensive Filtering:
  • Excludes removed posts
  • Excludes posts from banned users
  • Excludes reply posts
• Approval System Integration:
  • Maintains the same approval logic as the main group view
  • Auto-approves posts by approved members and moderators
• Chronological Display: Shows posts from newest to oldest
• Group Context: Each post shows which group it belongs to with a direct link

Visual Elements

• Added Feed link in the header with appropriate icon
• Added group indicators on posts
• Maintained post interaction capabilities (reactions, nutzaps, etc.)
• Added "View in group" links to see posts in their original context

UI/UX Considerations

• Consistent styling with the rest of the application
• Mobile-friendly design with responsive elements
• Clear status indicators (approved vs pending posts)
• Empty state handling for users with no groups or no posts

Testing Done

• Tested with multiple groups and posts
• Verified correct display of posts from different groups
• Confirmed post interactions work as expected
• Validated post filtering based on approval status

Closes #362