Add loading skeletons across dashboard, passes, guilds, members, and activity pages

[Lakes41]

Difficulty: Intermediate
Type: UI/UX

Background
Currently, data (even mock data) likely renders instantly or with a blank/flash state, since there's no shared loading pattern across routes.

Problem
When data fetching is eventually async (real API), the UI has no consistent loading state, and even now, page transitions can flash empty content, hurting perceived performance and polish.

Expected outcome
Each main route (/dashboard, /passes, /guilds, /members, /activity) shows a skeleton loader matching its layout while data is loading, using Next.js 14's loading.tsx convention.

Suggested implementation

• Create a shared Skeleton primitive component styled with Tailwind.
• Add loading.tsx files per route segment under apps/dashboard/app/.
• Compose route-specific skeletons (table skeleton, stat-card skeleton, list skeleton) from the shared primitive.

Acceptance criteria

• Each of the five main routes has a matching skeleton loading state
• Skeletons visually match the loaded layout (same grid/column structure)
• No layout shift (CLS) when content replaces the skeleton

Likely affected files/directories

• apps/dashboard/app/**/loading.tsx
• apps/dashboard/components/ (new shared Skeleton component)