Dashboard: read and persist dashboard / front-wall layout

[Adron]

Endpoints (bearer-verified 2026-09-15)

• GET/PUT /api/user/dashboard-layout → 200 {"layout":null} when unset
• GET/PUT /api/user/front-wall-layout → 200 {"layout":null}
• Both also arrive inline on GET /api/user as dashboardLayout / frontWallLayout

Acceptance criteria

• Service methods for both, with the layout kept as raw JSON — it is a web-oriented structure and must round-trip untouched.
• CurrentUser gains DashboardLayout and FrontWallLayout.
• A null layout is a valid "not configured" state, not an error.
• The app does not invent its own layout schema; if it renders a dashboard it interprets the server's, and writes back only what it understands.
• CLAUDE.md corrected to remove the 401 claim.