feat: KBX v60 Phase 4 complete — KbxQuantityField + index exports

Add KbxQuantityField (increment/decrement spinner) + update index exports
for all Phase 3.5–4 components (wrapper, form, specialized fields).

Components shipped:
- KbxScreenFrame, KbxTemplateStateBoundary, KbxSummaryBar (wrapper)
- KbxFormGrid, KbxFormSection (layout)
- KbxInput, KbxSelect, KbxDateField, KbxNumberField, KbxTextarea, KbxCheckbox (basic fields)
- KbxMoneyField, KbxQuantityField, KbxRadio (specialized fields)
- 9 template/composite/advanced (T02, T03, T06, T07, DataGrid, Dialog, Drawer, Tabs, Lookup)

Total Phase 1–4: 30 components, ~3500 LOC, contracts, registries, composables, tokens, app init complete.
Ready for page implementation using KbxScreenFrame wrapper pattern.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

frontend/src/shared/@kbx/contracts/command.ts

@@ -0,0 +1,21 @@
+/**
+ * Command Definition Contracts — v60
+ * Screen commands (Save, Delete, Approve, etc.)
+ */
+
+export type KbxCommandGroup = 'query' | 'edit' | 'workflow' | 'output' | 'more'
+
+export type KbxCommandVariant = 'primary' | 'secondary' | 'danger' | 'ghost'
+
+export type KbxRecipePermissionKind = 'none' | 'write' | 'execute'
+
+export interface KbxCommandDefinition {
+  id: string
+  label: string
+  group: KbxCommandGroup
+  shortcut?: string
+  variant?: KbxCommandVariant
+  permissionKind: KbxRecipePermissionKind
+  icon?: string
+  disabled?: boolean
+}