Display backend validation errors when submitting the form

[sergei-maertens]

Closes open-formulieren/open-forms#4510 - requires the backend PR to be merged as that changes the API endpoint used here.

I've opted to collect all the errors at the top and group them by step, rather than trying to weave this in the summary table. User research from Utrecht showed that this was the best way to show validation errors.

Ideally, there would be some aria-describedby options, but that requires a lot more work to link everything together.

[codecov]

Bundle Report

Changes will increase total bundle size by 6.18kB (0.06%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
@open-formulieren/sdk-OpenForms-umd	4.78MB	3.12kB (0.07%) ⬆️
@open-formulieren/sdk-esm	4.75MB	3.07kB (0.06%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: @open-formulieren/sdk-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/sdk-*.js	2.03kB	1.01MB	0.2%
assets/nl-*.js	518 bytes	23.36kB	2.27%
assets/en-*.js	518 bytes	22.5kB	2.36%

Files in assets/sdk-*.js:

• ./src/components/FormProgressIndicator.jsx → Total Size: 2.8kB

• ./src/components/Summary/ValidationErrors.jsx → Total Size: 3.75kB

• ./src/components/Form.jsx → Total Size: 2.81kB

• ./src/components/Summary/GenericSummary.jsx → Total Size: 3.19kB

• ./src/components/Summary/SubmissionSummary.jsx → Total Size: 3.76kB

Files in assets/nl-*.js:

• ./src/i18n/compiled/nl.json → Total Size: 25.75kB

Files in assets/en-*.js:

• ./src/i18n/compiled/en.json → Total Size: 24.88kB

view changes for bundle: @open-formulieren/sdk-OpenForms-umd

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
open-*.js	3.12kB	3.49MB	0.09%

Files in open-*.js:

• ./src/components/Summary/GenericSummary.jsx → Total Size: 3.19kB

• ./src/i18n/compiled/en.json → Total Size: 26.91kB

• ./src/components/Summary/ValidationErrors.jsx → Total Size: 3.75kB

• ./src/components/Summary/SubmissionSummary.jsx → Total Size: 3.76kB

• ./src/components/Form.jsx → Total Size: 2.81kB

• ./src/i18n/compiled/nl.json → Total Size: 25.75kB

• ./src/components/FormProgressIndicator.jsx → Total Size: 2.8kB

[codecov]

Codecov Report

Attention: Patch coverage is 87.17949% with 5 lines in your changes missing coverage. Please review.

Project coverage is 83.88%. Comparing base (775bb98) to head (483b4dd).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/components/Summary/SubmissionSummary.jsx	70.00%	3 Missing ⚠️
src/components/Summary/ValidationErrors.jsx	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #792      +/-   ##
==========================================
+ Coverage   83.67%   83.88%   +0.20%     
==========================================
  Files         244      245       +1     
  Lines        4777     4808      +31     
  Branches     1268     1272       +4     
==========================================
+ Hits         3997     4033      +36     
  Misses        747      747              
+ Partials       33       28       -5     

Flag	Coverage Δ
storybook	77.48% <91.66%> (+1.23%)	⬆️
vitest	62.70% <32.35%> (-0.30%)	⬇️

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[vaszig]

Nothing to add/mention!