feat(proxy): add image tracing endpoint

Add GET /trace which fetches an image, traces it into a vector shape, and returns the result BSON-encoded. Tracing is configurable via mode (alpha, bw, color) and format (shape, svg). The shape format parses the vtracer SVG into an outline/holes polygon matching @tts/mesh's Shape interface.

apps/proxy/package.json

@@ -16,7 +16,11 @@
     "@hono/node-server": "^1.13.7",
     "@tts/shared": "workspace:*",
     "@tts/tts": "workspace:*",
+    "@visioncortex/vtracer": "1.0.0-alpha.3",
+    "bson": "^6.10.4",
     "hono": "^4.6.14",
+    "sharp": "^0.35.3",
+    "svgpath": "^2.6.0",
     "zod": "^3.24.1"
   },
   "devDependencies": {