docs: fix broken links to Update channels page and fix HEIC image (#10880)

- Fix broken link references pointing to non-existent /admin/deployment/deployments
  page, redirect them to /admin/deployment/index (Mintlify docs)
- Fix broken link references in old docs (environments.mdx) using wrong path prefix
- Fix broken image on Update channels section: the ucarecdn asset is in HEIC format
  which browsers cannot render; append -/format/auto/ to serve as JPEG

Fixes CUB-2581

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

Author: keydunov