Kanban Board App

Build a kanban task management app with the following features:

**Boards:**
- User dashboard shows all boards they own or are members of
- Create a new board: name, description, visibility (Private / Team / Public)
- Board cover colour or image

**Lists:**
- Boards contain multiple lists (e.g. Backlog, In Progress, Review, Done)
- Add/rename/delete/reorder lists via drag
- Lists can be archived

**Cards:**
- Add a card to any list: title, description (rich text), due date, labels, assignees, checklist, attachments
- Drag a card between lists (snap into place)
- Click to open a card modal with all metadata, comments, and activity history

**Collaboration:**
- Invite teammates to a board by email
- Mention users in comments (@name) — they get a notification
- Real-time updates: when someone moves a card, every open board updates within a second (Supabase Realtime)

**Filters:**
- Filter bar above the board: by assignee, label, due date, text search
- Cards hide smoothly when filtered out (fade + collapse)

**Keyboard Shortcuts:**
- N: new card in focused list
- /: focus search
- Esc: close modal
- Arrow keys to navigate between cards

**Design:**
- Horizontal scrolling board with fixed sidebar
- Light and dark theme toggle
- Responsive: on mobile, lists stack vertically and cards show full-width

Store everything in Supabase. Use Supabase Realtime for cross-user card moves. RLS so only board members can read/write.