feat(mcp): implement 19 scene query and mutation tools

Scene querying: get_scene, get_node, describe_node, find_nodes, measure.
Scene mutation (undoable, atomic): apply_patch, create_level, create_wall,
place_item, cut_opening, set_zone, duplicate_level, delete_node.
Undo/redo: undo, redo.
Export: export_json, export_glb (not_implemented stub).
Validation: validate_scene, check_collisions.

Each tool has:
- Exported Zod input + output schemas
- register<Tool>(server, bridge) wiring function
- Bun test with happy-path + error-path coverage via InMemoryTransport

59 tool tests, all passing end-to-end through MCP protocol.

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

packages/mcp/src/tools/create-level.ts

@@ -0,0 +1,61 @@
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import type { AnyNodeId } from '@pascal-app/core/schema'
+import { LevelNode } from '@pascal-app/core/schema'
+import { z } from 'zod'
+import type { SceneBridge } from '../bridge/scene-bridge'
+import { ErrorCode, throwMcpError } from './errors'
+import { NodeIdSchema } from './schemas'
+
+export const createLevelInput = {
+  buildingId: NodeIdSchema,
+  elevation: z.number().optional(),
+  height: z.number().optional(),
+  label: z.string().optional(),
+}
+
+export const createLevelOutput = {
+  levelId: z.string(),
+}
+
+export function registerCreateLevel(server: McpServer, bridge: SceneBridge): void {
+  server.registerTool(
+    'create_level',
+    {
+      title: 'Create level',
+      description:
+        'Create a new level node attached to the given building. height and label are stored in metadata.',
+      inputSchema: createLevelInput,
+      outputSchema: createLevelOutput,
+    },
+    async ({ buildingId, elevation, height, label }) => {
+      const parent = bridge.getNode(buildingId as AnyNodeId)
+      if (!parent) {
+        throwMcpError(ErrorCode.InvalidParams, `Building not found: ${buildingId}`)
+      }
+      if (parent.type !== 'building') {
+        throwMcpError(
+          ErrorCode.InvalidParams,
+          `Node ${buildingId} is a ${parent.type}, expected building`,
+        )
+      }
+
+      const metadata: Record<string, unknown> = {}
+      if (height !== undefined) metadata.height = height
+      if (label !== undefined) metadata.label = label
+
+      const levelNode = LevelNode.parse({
+        level: elevation ?? 0,
+        children: [],
+        ...(Object.keys(metadata).length > 0 ? { metadata } : {}),
+        ...(label !== undefined ? { name: label } : {}),
+      })
+
+      const id = bridge.createNode(levelNode, buildingId as AnyNodeId)
+      const payload = { levelId: id as string }
+      return {
+        content: [{ type: 'text' as const, text: JSON.stringify(payload) }],
+        structuredContent: payload,
+      }
+    },
+  )
+}