Collections list and Add collection on the Configuration page

[ashleythedeveloper]

What

Collections list section on the Configuration page per Figma: table of collections (Name, Last updated, Files count, drill-in arrow) plus an "Add collection" input + button.

Acceptance criteria

• Collections list renders via the Collections CRUD API (Epic G3 #G3.2 ships this).
• Columns match Figma: Name, Last updated, Files count.
• Each row has a drill-in chevron that routes to the per-collection drill-in page (G6.4).
• "Add collection" form creates a new collection via API; appears in the list on success.

Sub-issue of Epic G6. Blocked by G3.2 (Collections CRUD API).