UI: Build Board view to display papers and voting

[lucianfialho]

Problem

There's no way to view a single board with all its papers. Users need a dedicated page to see board contents and vote on papers within the context of that collection.

Solution

Create a Board detail page showing all papers in the collection with board-specific voting and contributor info.

Acceptance Criteria

• New page route: /boards/[id] or similar

  • Fetch board + papers via GET /api/boards/[id]
  • Handle 404 if board not found
  • Show limited view for non-members (viewers can see public boards)

• Board header section:

  • Title + description
  • Paper count
  • Collaborators list/avatars
  • Edit board button (owner only)
  • Add paper button (editor+ only)
  • Share button

• Papers display:

  • Grid or list of papers in the board
  • Paper cards show:
    • Title, authors, arxivId
    • Quick preview of abstract
    • Board-specific vote count (separate from annotation votes)
    • Upvote button (click to vote)
    • Link to open full paper

• Sort/filter options:

  • Sort by: date added, title, vote count
  • Quick category filter if papers have categories
  • Search papers within board

• Add paper modal:

  • Search field (arXiv ID, DOI, or paper title)
  • Auto-fetch paper if not in system
  • Optional notes field
  • Add to board button

• Board voting system:

  • Separate from annotation upvotes
  • Idempotent (can't double vote)
  • Show vote count per paper
  • Highlight voted papers for current user

Dependencies

• Issue API: Implement Board CRUD endpoints #2: Board CRUD endpoints
• Issue API: Implement Board paper management endpoints #3: Board paper management endpoints

Design Notes

• Similar visual style to existing paper cards and annotation displays
• Responsive layout (mobile-friendly)
• Maintain dark theme consistency

Notes

• Consider if board voting is per-paper or if it impacts paper's global popularity
• May need aggregation logic for vote counts vs annotation upvotes