feat(spec): ADR-0047 — Interface section in the page authoring form

Adds the 'Interface (list pages)' section to the Studio page form,
visible when type == 'list': the interfaceConfig composite renders the
full Airtable-right-panel equivalent — Source/Source View (iron-rule
help text), Levels, Filter By rows, Appearance (Show Description +
Allowed Visualizations tags), User Filters (Element style + Fields rows
with showCount) and User Actions toggles.

Completes the phase-5 authoring surface: views got their End-user
controls section in #1792; pages now have the same for interface mode.
Browser-verified in Studio against the showcase Task Workbench page.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: os-zhuang

packages/spec/src/ui/page.form.ts

@@ -39,6 +39,21 @@ export const pageForm = defineForm({
         { field: 'regions', type: 'repeater', required: true, helpText: 'Layout regions (header, main, sidebar, footer) with components' },
       ],
     },
+    {
+      label: 'Interface (list pages)',
+      description: 'ADR-0047 interface mode: bind a source view and curate the end-user surface — quick filters, locked visualizations, toolbar actions (Airtable Interfaces parity).',
+      collapsible: true,
+      collapsed: true,
+      visibleOn: "data.type == 'list'",
+      fields: [
+        {
+          field: 'interfaceConfig',
+          type: 'composite',
+          helpText:
+            'source/sourceView bind the object view (columns, base filter and sort are inherited — the iron rule); userFilters picks the element style (dropdown / tabs / toggle) and exposed fields; appearance.allowedVisualizations whitelists renderers (one entry = locked); userActions toggles the toolbar.',
+        },
+      ],
+    },
     {
       label: 'Advanced',
       description: 'Activation, audience, and accessibility.',