Add real screenshots to all Admin UI pages

[anton62k]

Summary by cubic

Replaced placeholders with real screenshots across the Admin UI docs and aligned copy with the current UI. Adds 24 screenshots over 8 pages for clearer, task-focused guidance.

• Refactors
  • Assets: gallery screenshot with search and type/status/size filters.
  • Branches & History: screenshots for branch list, create dialog, and branch map; simplified revision flow.
  • Changes & Diff: screenshots for row changes list, full summary, and field-level diff; clearer commit/revert steps.
  • Endpoints: screenshots for API tabs and custom endpoint creation; documented Draft/Head toggles; moved sidebar position to 8.
  • Migrations: history view and Apply from JSON/Branch; moved sidebar position to 7.
  • Row Editor: screenshots for form, JSON, FK navigation, and file fields; clarified behaviors.
  • Schema Editor: screenshots for editor, add field, FK, nested objects, and JSON view.
  • Table Editor: screenshots for columns, column menu, views, filter, and sort; updated row actions; removed outdated admin-ui-table-editor.png.

^{Written for commit 43f84f5. Summary will update on new commits.}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud