DEVEX-744: Form validation for the Template Builder customizations step

Problem

In the new Template Builder wizard, creating a template with no organization selected produces an unhelpful backend error (empty organization_id sent to the API). There is no client-side validation on the final "Customizations" step: computeCanContinue only checks name and provisioner availability, so the "Create Template" button is enabled even when the organization is missing.

The customizations form is a horizontal two-column grid. Showing per-field inline errors (Formik helperText) would push fields down and break column alignment. We want validation before submit, with messages aggregated at the top of the step rather than inline under fields.

Decision (confirmed with user)

• Formik-wrap the customizations step (idiomatic, mirrors the old CreateTemplateForm), rather than ad-hoc reducer validation.
• Validate organization + all required fields (organization, template ID/name, plus display name/description/icon format limits), reusing the shared Yup validators in utils/formUtils.ts.

Approach

Make TemplateCustomizationsStep a Formik form that is the source of truth for the five customization fields. Validate on submit; render an aggregated error summary Alert at the top of the step. Connect the wizard's existing "Create Template" button (which lives in the parent nav bar) to the child form using the standard form="<id>" type="submit" HTML association, so no imperative handle or extra callback is needed. Only valid submits reach the API.

Steps

1. TemplateCustomizationsStep.tsx: convert to Formik with a Yup schema (nameValidator, displayNameValidator, description max 128, iconValidator, organization always required); initial values seeded from wizard state; aggregated error Alert at the top; keep provisioner reporting and org auto-select.
2. TemplateBuilderPageView.tsx: wire the last-step button to submit the form via the form attribute; add an onCreate prop; relax the customizations continue gate to the provisioner check.
3. wizardState.ts: toCreateTemplateRequest(state, customizations) composes the request from base/modules in state plus submitted values.
4. TemplateBuilderPage.tsx: adapt handleCreate.

Behavior notes

• A genuinely invalid organization still surfaces the backend's message via the existing createError alert; only the empty-org case is caught client-side.
• Unsaved edits to display name/description/icon are discarded when navigating Back off the last step (Formik unmounts and re-seeds from base defaults), matching the wizard's existing reset semantics.

Post-plan refinements (from review)

• Organization is unconditionally required (removed the conditional orgRequired), since the page is permission-gated and always has at least one permitted org.
• toCreateTemplateRequest keeps the submitted form values authoritative (no fallback to state, which would resurrect optional fields a user deliberately cleared).
• Removed the now-dead organizationId field from the reducer state.
• Story reuses the real query-key builders and the shared Button component.

Testing

• Storybook interaction tests for the customizations step (missing org, missing name, single-org auto-select, valid submit).
• Updated wizardState.test.ts for the new toCreateTemplateRequest signature.