feat(17-02): repeater field and dependent dropdown states

- RepeaterField: rows with drag handle, index, titleFrom title, error chip,
  move up/down (buttons, ArrowUp/ArrowDown on the handle, native drag and
  drop), expand/collapse, remove (asks only for a row holding a value),
  add with nested defaults, maxItems counter, empty state, collapse all;
  every change edits form state only
- 422 row paths (content.3.answer) open the row, mark it and focus the
  nested control; the banner no longer repeats row messages
- DropdownField dependsOn: waiting, loading, not used, empty, loaded with
  depth indent, failed with retry; cached per sibling value, last request
  wins, a stale value is cleared after a sibling change and announced
- FormView provides form feedback (errors and notices by row path, the
  polite live region, its confirm dialog) and the options cache; FormGrid
  provides the sibling scope for repeater rows
- repeater.* and form.dependent_* phrase keys (en, pl), smoke specs, docs

admin/src/components/form/FormGrid.vue

@@ -1,12 +1,17 @@
 <script setup lang="ts">
+import { computed, provide } from 'vue'
 import type { AdminRecord, ControllerParams, FormField as FormFieldSchema, RecordMeta } from '../../api/types'
 import FormField from './FormField.vue'
+import { FIELD_SCOPE } from './formContext'
 import { RELATION_MANAGER } from './registry'
 
 // Two-column form grid (design screen 4): span left -> column 1, right ->
 // column 2, full (Winter's default) -> the whole row, auto and row -> the next
 // free slot. Below 600px everything is one column. Gaps are 22px x 24px.
-defineProps<{
+// The grid is the scope its fields read siblings from (a dependent dropdown,
+// D-08); a repeater row's grid passes `scopePath`, the repeater's name, so a
+// nested field's routes address it as `<repeater>.<field>`.
+const props = defineProps<{
   fields: FormFieldSchema[]
   values: AdminRecord
   errors: Record<string, string[]>
@@ -16,9 +21,17 @@ defineProps<{
   source?: ControllerParams | null
   recordId?: number | null
   idPrefix?: string
+  /** The repeater whose row this grid renders. */
+  scopePath?: string
 }>()
 const emit = defineEmits<{ update: [name: string, value: unknown] }>()
 
+provide(FIELD_SCOPE, {
+  fields: computed(() => props.fields),
+  values: computed(() => props.values),
+  path: (name: string) => (props.scopePath ? `${props.scopePath}.${name}` : name),
+})
+
 function spanClass(field: FormFieldSchema): string {
   // The relation manager always takes the whole row (design screen 5).
   if (field.type === RELATION_MANAGER) {