Add activity API pagination and filtering

[GarbageBoy8]

Summary

Closes #47

Adds bounded pagination and filtering support to activity retrieval so the audit log
remains usable as webhook and simulated events grow.

Changes

• Added an activity query contract with limit, cursor, type, source,
  severity, entityType, actor, and from
• Updated activity storage/service to return paginated results with nextCursor
• Updated /api/activity to validate query parameters and return filtered activity
  results
• Updated the activity page with visible filters and paginated loading
• Added a clear empty state for filtered results
• Added tests for pagination, filters, empty results, and invalid query parameters

Testing

npx pnpm --filter @guildpass/dashboard typecheck
npx pnpm --filter @guildpass/dashboard test
npx pnpm --filter @guildpass/dashboard lint
npx pnpm --filter @guildpass/dashboard build

## Notes

lint passes with one existing warning for WebhookPayload.data: Record<string, any>.


Skipped: no extra dependencies, no DB persistence. Add when activity storage moves
from in-memory to a real backend.

[Lakes41]

Good Job, Do resolve conflicts @GarbageBoy8

[Lakes41]

@GarbageBoy8 Do resolve conflicts, I might have to take you off when it 24 hours