Group inventory: add read-only panel using shared inventory components

[prodmodfour]

Goal

Render the authoritative group inventory document in the new page using the reusable inventory components.

Scope

• Add GroupInventoryPanel.vue or equivalent.
• Call the load API from the group inventory page.
• Render money, section tabs, section counts, and inventory rows.
• Keep player and GM behavior read-only in this ticket.
• Reuse the generic inventory table and section tab components.

Acceptance criteria

• Loading, error, and empty inventory states are visible and accessible.
• The page renders all inventory sections with normalized data from the server.
• Players and GMs can both view the shared inventory.
• No direct editing, saving, or transfers are added in this ticket.

Depends on

• Group inventory: add load API route and client route constants #30
• Inventory UI: extract reusable section tabs from trainer inventory panel #33
• Group inventory: add page shell and navigation entry #34