chore(server): add zod dep for McpServer migration (Phase 0)

Phase 0 of the Server→McpServer + valibot→Zod migration. A throwaway POC
(deleted) validated the target pattern over raw stdio: McpServer with a
registration loop + shared dispatch callback, Zod raw-shape inputSchema
auto-generating the tools/list JSON Schema with field descriptions
(.describe() preserved) and required/optional/min-max intact, registerPrompt
for figma_to_code, edge validation rejecting bad args (-32602), and no
deprecated Server symbol. zod is pinned to ^4.4.3 to match the SDK's resolved
peer (no dual version).

Author: awdr74100

packages/server/package.json

@@ -30,7 +30,8 @@
     "@msgpack/msgpack": "^3.1.3",
     "oxc-parser": "^0.133.0",
     "valibot": "^1.4.0",
-    "ws": "^8.20.1"
+    "ws": "^8.20.1",
+    "zod": "^4.4.3"
   },
   "devDependencies": {
     "@types/ws": "^8.18.1",