[FEATURE] Add Cursor-Based Pagination

[JoshuaAFerguson]

Objective

Replace offset pagination with cursor-based pagination for better performance.

Implementation

type PaginatedResponse struct {
    Data   []Session `json:"data"`
    Cursor string    `json:"next_cursor,omitempty"`
    Total  int       `json:"total"`
}

// GET /sessions?cursor=eyJ...&limit=50

Benefits

• Consistent results (no duplicates/missing items)
• Better performance for large datasets
• Works with real-time data

Acceptance Criteria

• All list endpoints support cursor pagination
• Backward compatible with offset pagination
• Documentation updated
• UI updated

Files

• api/internal/pagination/cursor.go (NEW)
• All list handler files