feat(mcp): add resources and prompts

Resources: pascal://scene/current (JSON), /scene/current/summary
(markdown with per-level counts, floor areas, bbox), /catalog/items
(returns catalog_unavailable in headless mode), and the templated
pascal://constraints/{levelId} which exposes slabs + wall footprints
via @pascal-app/core/wall helpers.

Prompts: from_brief (generate scene from a natural-language brief),
iterate_on_feedback (minimal-diff patch proposals), and
renovation_from_photos (orchestrates the vision tools).

17 tests, all passing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/mcp/src/resources/catalog-items.ts

@@ -0,0 +1,39 @@
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import type { SceneBridge } from '../bridge/scene-bridge'
+
+/**
+ * `pascal://catalog/items` — item catalog (if the host supplies one).
+ *
+ * `@pascal-app/core` does NOT expose a runtime item catalog — that is the host
+ * app's responsibility. In headless / standalone MCP mode we therefore return
+ * a stable, machine-readable "unavailable" payload so agents can detect this
+ * and fall back to free-form item creation.
+ */
+export function registerCatalogItems(server: McpServer, _bridge: SceneBridge): void {
+  server.registerResource(
+    'catalog-items',
+    'pascal://catalog/items',
+    {
+      title: 'Item catalog',
+      description:
+        'Catalog of placeable items. Not available in core; the host app is expected to override this resource when it has a catalog.',
+      mimeType: 'application/json',
+    },
+    async (uri) => {
+      const payload = {
+        status: 'catalog_unavailable' as const,
+        items: [] as never[],
+        note: '@pascal-app/core does not ship a runtime item catalog; the host app is expected to provide one by overriding this resource.',
+      }
+      return {
+        contents: [
+          {
+            uri: uri.href,
+            mimeType: 'application/json',
+            text: JSON.stringify(payload),
+          },
+        ],
+      }
+    },
+  )
+}