fix(media): count whole library for "All Files" total

[PlusA2M]

Description

The Media library sidebar always shows All Files (24) because the GET /admin/media
handler reports the page length as the total. This computes the real total with a
COUNT(*) over the same filters.

Fixes #888

Changes

• admin-media.ts GET /: add a COUNT(*) over the same folder/type conditions
  (without LIMIT/OFFSET) and use it for totalFiles.
• Compute hasNextPage from offset + results.length < totalFiles instead of
  comparing the page length to the limit.
• Add a regression test asserting the total comes from COUNT(*) (not the page
  size), that folder/type filters flow into the count query, and that
  hasNextPage is false on the last page.

Testing

Unit Tests

• Added/updated unit tests (admin-media-total-count.test.ts)
• All unit tests passing (npm test — full suite green)

E2E Tests

• Added/updated E2E tests
• All E2E tests passing

Checklist

• Code follows project conventions
• Tests added/updated and passing
• Type checking passes
• No console errors or warnings
• Documentation updated (if needed) — n/a

[lane711]

Thanks for this fix! We're in the process of merging v3 to main — v3 has migrated the media module to a document model architecture (MediaDocumentService), so admin-media.ts no longer queries the legacy media table directly. The totalFiles bug you identified does exist in v3, but the fix needs to go into MediaDocumentService.list() to return a real total count alongside the page results. We'll track this as a v3 issue and fix it natively. Really appreciate the detailed PR and regression test — it made diagnosing the v3 equivalent much easier.