refactor: share trace, error boundary, and proxy http helpers

Lift the trace-to-shape geometry into @tts/mesh (traceToShape/
traceToUvBounds), parameterized by scale so the web token viewer and
@tts/tabletop share one implementation. Move the CORS proxy HTTP helpers
(assetUrl, resolveAssetUrl, traceImage) into a new @tts/http package, and
make @tts/tabletop's ErrorBoundary the single source used by the web app.

This removes the duplicated ErrorBoundary, assetUrl, tabletopHttp, and
trace-to-shape code from apps/web and packages/tabletop.

apps/web/package.json

@@ -22,6 +22,7 @@
     "@tts/mesh": "workspace:*",
     "@tts/shared": "workspace:*",
     "@tts/bgm": "workspace:*",
+    "@tts/http": "workspace:*",
     "@tts/tabletop": "workspace:*",
     "bson": "^7.3.1",
     "react": "^19.2.8",