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/set-zone.ts

@@ -0,0 +1,56 @@
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
+import type { AnyNodeId } from '@pascal-app/core/schema'
+import { ZoneNode } 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 setZoneInput = {
+  levelId: NodeIdSchema,
+  polygon: z.array(Vec2Schema).min(3),
+  label: z.string().min(1),
+  properties: z.record(z.string(), z.unknown()).optional(),
+}
+
+export const setZoneOutput = {
+  zoneId: z.string(),
+}
+
+export function registerSetZone(server: McpServer, bridge: SceneBridge): void {
+  server.registerTool(
+    'set_zone',
+    {
+      title: 'Set zone',
+      description:
+        'Create a polygonal zone on the given level. label is stored as the zone name and properties are merged into metadata.',
+      inputSchema: setZoneInput,
+      outputSchema: setZoneOutput,
+    },
+    async ({ levelId, polygon, label, properties }) => {
+      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 zone = ZoneNode.parse({
+        name: label,
+        polygon,
+        metadata: properties ?? {},
+      })
+      const id = bridge.createNode(zone, levelId as AnyNodeId)
+
+      const payload = { zoneId: id as string }
+      return {
+        content: [{ type: 'text' as const, text: JSON.stringify(payload) }],
+        structuredContent: payload,
+      }
+    },
+  )
+}