fix: make @mariozechner/clipboard optional for ARM compatibility

Fixes #4596

The clipboard package doesn't provide native binaries for linux-arm-gnueabihf
(32-bit ARM). Since OpenClaw has its own clipboard implementation and doesn't
rely on pi-coding-agent's clipboard functionality, we can safely make this
an optional dependency.

This allows OpenClaw to run on 32-bit Raspberry Pi systems without
encountering the 'Cannot find module' error during startup.

package.json

@@ -209,6 +209,7 @@
     "zod": "^4.3.6"
   },
   "optionalDependencies": {
+    "@mariozechner/clipboard": "^0.3.0",
     "@napi-rs/canvas": "^0.1.88",
     "node-llama-cpp": "3.15.0"
   },