Body tracking: head/hands/feet drive the interactive families

MediaPipe PoseLandmarker (BlazePose lite) integrated fully offline: the
WASM runtime and the bundled .task model are served to the renderer over
a new djvres:// protocol (fetch does not work on file://), with
'wasm-unsafe-eval' added to the output CSP. pose.js exposes PoseTracker;
interactive.js detects at ~30 Hz, maps landmarks into mirrored
cover-fitted screen space and smooths them with velocities.

Upgrades when a body is tracked (silent fallback to motion otherwise):
- all physical modes: moving head/hands/feet stamp precise motion blobs
- Sciame: the swarm follows your head
- Interattivo Modello: hand swipes spin the robot, it leans toward your
  head, raising a hand fast makes it jump
- Silhouette: neon skeleton (bones + joints + glowing head) over the
  electric outline

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

package.json

@@ -26,11 +26,15 @@
       "main.js",
       "preload.js",
       "src/**/*",
-      "svg/**/*"
+      "svg/**/*",
+      "models/**/*"
     ]
   },
   "devDependencies": {
     "electron": "^33.4.11",
     "electron-builder": "^24.13.3"
+  },
+  "dependencies": {
+    "@mediapipe/tasks-vision": "^1.0.0"
   }
 }