Kanban board view: show task due dates and colored tags on cards

[virtuarsys]

The Kanban board view (folder = list, note = card) is great for organizing tasks visually, but cards don't surface information that's essential for using it as an actual task-management tool rather than just a visual note organizer.

1. Due date indicator on cards. Two cases:

• When a note has a due date/reminder set (the bell icon in the toolbar), the card should show it.
• When a note is a tasklist with individual tasks that have due dates, the card should show at least the next upcoming due date.
  In both cases, overdue items should ideally be flagged visually (e.g. red text/badge). Right now, neither case shows anything on the card, even though the data already exists.

2. Colored tags. Tags currently render in a single neutral gray on cards, making it hard to visually distinguish categories at a glance. Letting users assign a color per tag (like most Kanban/task tools) would make the board scannable at a glance.