refactor(frontend): read the panel's navigation from one route manifest (#6922)

The router, the sidebar, the page titles and the command palette each kept
their own list of the panel's pages, so a page added to one could go
missing from another without any test noticing. They all read
src/routes/panelRoutes.tsx now, and a contract test holds the manifest to
the router, the translation bundle and the palette keywords.

The unused useZodForm helper goes, and CONTRIBUTING, frontend/CLAUDE.md and
the frontend README describe the useForm + rhfZodValidate pattern the
panel's forms actually use.

frontend/src/components/form/rhf/index.ts

@@ -1,5 +1,4 @@
 export { FormField, type FormFieldProps } from './FormField';
-export { useZodForm } from './useZodForm';
 export { rhfZodValidate } from './rhfZodValidate';
 export { normalizeAntdOnChange, type ValueProp } from './normalizeAntdOnChange';
 export { toDotted, type FieldName } from './toDotted';