chore(submodule): bump backend to 573457f

[juancobo]

Advances the backend pin over yesterday's five merged fixes:

• NEH-127 — GET /collections/{id}/hierarchy no longer 500s (backend Capture #32)
• NEH-51 — image upload size cap + orphan cleanup on failure (backend Capture workflow #33)
• NEH-130 — DB↔filesystem↔manifest integrity check, startup schema-head guard (backend Change of architecture #34)
• NEH-140 — project rename moves the whole capture tree (backend Sync docs #35)
• NEH-141 — atomic storage-override writes (backend Dev #36)

Pointer-only change; no superproject files touched.

[Copilot]

Pull request overview

Updates the backend submodule to include five merged fixes.

Changes:

• Fixes collection hierarchy counts and upload cleanup.
• Adds integrity/schema checks and safer project renames.
• Makes storage override writes atomic.