feat: add admin API requests log viewer page

[kiloconnect]

Summary

Adds an admin-only page at /admin/requests for searching and viewing API request logs from the api_request_log table. This is a walking skeleton — functional end-to-end.

Changes

Backend

• src/routers/admin-requests-router.ts — New tRPC router with list and getById procedures, protected by adminProcedure
  • list: Supports pagination, date range filtering (startTime/endTime), exact request ID match, and fulltext search (ILIKE across user ID, org ID, provider, model, and ID)
  • getById: Returns a single request log entry by ID
• src/routers/admin-router.ts — Mounted new router as requests

Frontend

• src/app/admin/requests/page.tsx — Server component page following existing admin page pattern
• src/app/admin/components/RequestsTable.tsx — Client component with URL-driven state, search filters (request ID, date range, fulltext), results table with color-coded status badges, and pagination
• src/app/admin/components/RequestDetailDialog.tsx — Detail dialog with "Overview" (structured fields) and "Raw JSON" tabs
• src/app/admin/api/requests/hooks.ts — tRPC query hooks
• src/app/admin/components/AppSidebar.tsx — Added "API Requests" link under Analytics & Observability

Tests

• src/routers/__tests__/admin-requests-router.test.ts — Tests for auth guard, list query shape, filters (requestId, date range, query search), pagination, and getById

How to Test

1. Log in as an admin user
2. Navigate to /admin/requests via the sidebar or directly
3. Try searching by request ID, date range, or fulltext query
4. Click a row to see the detail dialog with structured and raw JSON views

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