## What this PR does
Re-applies cozystack/cozystack-ui#26 (by @lexfrei) onto the in-tree
console, after the UI was vendored into the monorepo (#2963) and the
standalone repo is being archived. Part of the cozystack-ui retirement
tracked in #3097.
In the four backup create pages (Backup, BackupJob, BackupPlan,
BackupRestoreJob), the RJSF `SchemaForm.validate()` call now runs right
after the name check and before the page-level required-field alerts.
The submit button lives outside RJSF and bypasses its validation, so
each page triggers `validate()` explicitly; it previously ran only after
the manual alert checks, so a schema-required field left empty exited
via an alert without RJSF ever rendering its inline errors. Validating
first makes inline errors show consistently; the page-level alerts then
cover only page-only requirements (application/backup reference,
strategy, timestamp).
Scope is the validation-ordering change only — the original PR's
VMDisk/StorageClass parts were obsoleted by the `DynamicOptionsWidget`
refactor (#30) already present in the vendored snapshot.
## Verification
- Includes the original per-page regression tests.
- `pnpm typecheck` clean; full console suite green (317 passed).
Original PR: cozystack/cozystack-ui#26 — credited via `Co-authored-by`.
```release-note
NONE
```
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Improved submission validation across backup creation, backup job,
backup plan, and backup restore job pages.
* Inline required-field errors now appear before page-level alerts.
* Invalid submissions are prevented from sending requests or triggering
unnecessary alerts.
* **Tests**
* Expanded coverage for validation order and submission blocking.
* Improved form test scenarios for invalid and missing data.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
myasnikovdaniil
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