feat(17-01): repeater field type and the dependent dropdown save recheck

- cabana: type repeater with nested form.fields (text, textarea, number,
  checkbox, switch, dropdown, richeditor), prompt, minItems, maxItems,
  titleFrom; groups, style, nested repeaters and other types fail boot
- rows decoded before projection: only nested keys, coerced scalars,
  per-row required (field.index.nested), row bounds; ProjectWritableFields
  exempts repeater lists only, nestedValue unchanged
- nested richeditor values sanitized with notices under the row path
- dependent dropdowns rechecked on save, top level and per row; null when
  the sibling takes no choice, 422 form.dependent_invalid otherwise
- dependent-options accepts repeater.field; schema carries RepeaterForm
- backend lang repeater.max_items, repeater.min_items,
  form.dependent_invalid; TestCompanionsRepeaterSmoke; docs

modules/cabana/testdata/companions/models/link/fields.yaml

@@ -16,3 +16,26 @@ fields:
         label: Description
         type: richeditor
         size: large
+    rows:
+        label: Rows
+        type: repeater
+        prompt: Add row
+        titleFrom: title
+        maxItems: 5
+        form:
+            fields:
+                title:
+                    label: Title
+                    type: text
+                    required: true
+                body:
+                    label: Body
+                    type: richeditor
+                type:
+                    label: Type
+                    type: dropdown
+                    options: typeOptions
+                reference:
+                    label: Reference
+                    type: dropdown
+                    dependsOn: type