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-wall.ts

@@ -0,0 +1,57 @@
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import type { AnyNodeId } from '@pascal-app/core/schema'
+import { WallNode } from '@pascal-app/core/schema'
+import { z } from 'zod'
+import type { SceneBridge } from '../bridge/scene-bridge'
+import { ErrorCode, throwMcpError } from './errors'
+import { NodeIdSchema, Vec2Schema } from './schemas'
+
+export const createWallInput = {
+  levelId: NodeIdSchema,
+  start: Vec2Schema,
+  end: Vec2Schema,
+  thickness: z.number().positive().optional(),
+  height: z.number().positive().optional(),
+}
+
+export const createWallOutput = {
+  wallId: z.string(),
+}
+
+export function registerCreateWall(server: McpServer, bridge: SceneBridge): void {
+  server.registerTool(
+    'create_wall',
+    {
+      title: 'Create wall',
+      description:
+        'Create a new wall on the given level between two 2D points. Thickness and height default to the core library defaults when omitted.',
+      inputSchema: createWallInput,
+      outputSchema: createWallOutput,
+    },
+    async ({ levelId, start, end, thickness, height }) => {
+      const parent = bridge.getNode(levelId as AnyNodeId)
+      if (!parent) {
+        throwMcpError(ErrorCode.InvalidParams, `Level not found: ${levelId}`)
+      }
+      if (parent.type !== 'level') {
+        throwMcpError(
+          ErrorCode.InvalidParams,
+          `Node ${levelId} is a ${parent.type}, expected level`,
+        )
+      }
+
+      const wall = WallNode.parse({
+        start,
+        end,
+        ...(thickness !== undefined ? { thickness } : {}),
+        ...(height !== undefined ? { height } : {}),
+      })
+      const id = bridge.createNode(wall, levelId as AnyNodeId)
+      const payload = { wallId: id as string }
+      return {
+        content: [{ type: 'text' as const, text: JSON.stringify(payload) }],
+        structuredContent: payload,
+      }
+    },
+  )
+}