Create collapsable group sections in template

[Aidanpgh]

Description

Description:

Modify category template to render topics in collapsible date sections when grouped view is active. Pinned topics appear in their own pinned section at the top.

Acceptance Criteria:

1. Each date group has clickable header with a v shaped icon to indicated collision and expansion, label, and topic count
2. Pinned group appears first if pinned topics exist
3. Header click toggles collapse/expand with smooth animation
4. All sections expanded by default
5. Sections use existing topic list item template

Community forum reference

No response