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/get-node.ts

@@ -0,0 +1,37 @@
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import type { AnyNodeId } 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 getNodeInput = {
+  id: NodeIdSchema,
+}
+
+export const getNodeOutput = {
+  node: z.record(z.string(), z.unknown()),
+}
+
+export function registerGetNode(server: McpServer, bridge: SceneBridge): void {
+  server.registerTool(
+    'get_node',
+    {
+      title: 'Get node',
+      description: 'Return the full node payload for the given ID.',
+      inputSchema: getNodeInput,
+      outputSchema: getNodeOutput,
+    },
+    async ({ id }) => {
+      const node = bridge.getNode(id as AnyNodeId)
+      if (!node) {
+        throwMcpError(ErrorCode.InvalidParams, `Node not found: ${id}`)
+      }
+      const payload = { node: node as unknown as Record<string, unknown> }
+      return {
+        content: [{ type: 'text' as const, text: JSON.stringify(payload) }],
+        structuredContent: payload,
+      }
+    },
+  )
+}