fix: Dashboard crashes with blank white screen — systems.filter is not a function

[Pcmhacker-piro]

Summary
Fixes the Dashboard crash caused by calling .filter() on a paginated response object instead of the items array. The root cause was in ensureListResponse in api.ts which returned the full paginated wrapper { items, total, skip, limit } instead of extracting the items array.
Closes #309
Type of Change

• Bug fix
  Checklist
• I have read CONTRIBUTING.md
• My code follows the project style
• I have added/updated tests where relevant
• Tests/lint pass locally (if available)
• I have not committed .env or any secrets
• I have updated documentation if needed
  Root Cause
  The backend returns a paginated response: { items: [], total: 0, skip: 0, limit: 50 }. The ensureListResponse function in api.ts passed through the entire object instead of extracting .items. Consumers like Dashboard.tsx, Documents.tsx, and AISystems.tsx used the pattern Array.isArray(data) ? data : (data?.items ?? []) to handle both formats, but if the fallback was triggered on the paginated wrapper, the object itself was assigned to the variable — causing .filter() to throw "systems.filter is not a function".
  Fix

1. api.ts — ensureListResponse now always returns T[] by unwrapping data.items when the response is a paginated object (return type changed from union T[] | { items: T[]; ... } to T[])
2. Dashboard.tsx, Documents.tsx, AISystems.tsx — simplified extraction to (data ?? []) since the API now consistently returns a plain array
   CHANGED FILES

• frontend/src/services/api.ts — ensureListResponse now extracts and returns data.items instead of the whole paginated object; return type changed from T[] | { items: T[]; ... } to T[]
• frontend/src/pages/Dashboard.tsx — simplified systems and documents extraction from complex ternary to (data ?? [])
• frontend/src/pages/Documents.tsx — same simplification for documents and systems
• frontend/src/pages/AISystems.tsx — same simplification for systems
  COMMITS
  d47fd58 - fix: Dashboard crashes with blank white screen — systems.filter is not a function
  TESTING PERFORMED
  N/A (frontend lint/build tools not available locally; CI runs lint on push via GitHub Actions)
  FINAL STATUS
• Branch Name: fix/dashboard-systems-filter-crash
• Commit Hash: d47fd58
• PR Created: No (token lacks createPullRequest scope) — compare URL provided above
• Ready for Review: Yes

[Pcmhacker-piro]

@SdSarthak

Hi, the checks have passed. Could you please review and approve the pending workflows when you have a chance? Thank you!