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/schemas.ts

@@ -0,0 +1,48 @@
+import { z } from 'zod'
+
+/**
+ * Shared Zod schemas used by multiple MCP tools. Keep DRY — if a shape is
+ * referenced by more than one tool, define it here.
+ */
+
+/** A node identifier — non-empty string. The core uses `${prefix}_${nanoid}`. */
+export const NodeIdSchema = z.string().min(1)
+
+/** 2D point as [x, z] (floor plane). Matches core's tuple convention. */
+export const Vec2Schema = z.tuple([z.number(), z.number()])
+
+/** 3D point as [x, y, z]. */
+export const Vec3Schema = z.tuple([z.number(), z.number(), z.number()])
+
+/**
+ * A single patch operation. Union of create / update / delete.
+ *
+ * For `create`, the node object must include `type` so Zod can discriminate at
+ * the bridge layer — we accept a plain object here and let the bridge's Zod
+ * re-parse catch structural issues. For `update`, `data` is a partial merge.
+ */
+export const CreatePatchSchema = z.object({
+  op: z.literal('create'),
+  node: z.record(z.string(), z.unknown()),
+  parentId: NodeIdSchema.optional(),
+})
+
+export const UpdatePatchSchema = z.object({
+  op: z.literal('update'),
+  id: NodeIdSchema,
+  data: z.record(z.string(), z.unknown()),
+})
+
+export const DeletePatchSchema = z.object({
+  op: z.literal('delete'),
+  id: NodeIdSchema,
+  cascade: z.boolean().optional(),
+})
+
+export const PatchSchema = z.discriminatedUnion('op', [
+  CreatePatchSchema,
+  UpdatePatchSchema,
+  DeletePatchSchema,
+])
+
+export type Patch = z.infer<typeof PatchSchema>