tech debt: implement proper frontend pagination for servers, agents, and skills

Context

Issue #879 raised the API limit from 100 to 500 as a quick fix, but this is a ceiling that will eventually be hit. The frontend currently fetches a single page of results and has no mechanism to load more.

Current State

• Backend endpoints (/api/servers, /api/agents, /api/skills) support limit and offset query parameters and return total_count in the response
• Frontend calls each endpoint once with ?limit=500 and renders whatever comes back
• No "load more", infinite scroll, or page navigation exists in the UI

Proposed Solution

Implement client-side pagination in the Dashboard for all three asset types (servers, agents, skills):

1. Use total_count from the API response to detect when more items exist
2. Either fetch all pages in a loop on initial load, or add a "Load More" / infinite scroll pattern
3. Update useServerStats.ts to handle multi-page fetching
4. Consider adding a search/filter bar that uses the backend query parameter to reduce payload size

Acceptance Criteria

• All servers are visible in the UI regardless of total count
• All agents are visible in the UI regardless of total count
• All skills are visible in the UI regardless of total count
• No hardcoded limit caps the number of visible items