Board grouping and ordering

[samcorky]

Add support for better organisation of boards in the UI.

Group boards under headings

• Allow boards to be grouped under user-defined headings (e.g. "Work", "Personal", "Archived").
• Similar in concept to Authentik dashboard groups.
• Headings are purely organisational and do not affect board behaviour.

Re-order boards

• Allow boards to be manually re-ordered.
• The chosen order should be persisted across page reloads and sessions.
• Re-ordering should work both within a group and across groups (if grouping is enabled).

Notes

• Default behaviour should remain unchanged if grouping or custom ordering is not configured.

[sjefferson99]

Will add a group name column to the board table and a UI that can group on that or ignore it.
Will offer ordering by created date (when implemented), alphabetically and custom. Will introduce an order column into the board table similar to card and UI will order and group as per these preferences on that page.