ui/phase-9: PixiJS map renderer with torus and no-wrap modes

Stand up the vector map renderer in ui/frontend/src/map/ on top of
PixiJS v8 + pixi-viewport@^6. Torus mode renders nine container
copies for seamless wrap; no-wrap mode pins the camera at world
bounds and centres on an axis when the viewport exceeds the world
along that axis. Hit-test is a brute-force pass with deterministic
[-priority, distSq, kindOrder, id] ordering and torus-shortest
distance, validated by hand-built unit cases.

The development playground at /__debug/map exposes a window
debug surface for the Playwright spec, which forces WebGPU on
chromium-desktop, WebGL on webkit-desktop, and accepts the
auto-picked backend on mobile projects.

Algorithm spec lives in ui/docs/renderer.md, which also pins the
new deprecation status of galaxy/client (the entire Fyne client
module, including client/world). client/world/README.md and the
Phase 9 stub in ui/PLAN.md gain matching deprecation banners.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/frontend/package.json

@@ -13,7 +13,9 @@
   },
   "dependencies": {
     "flatbuffers": "^25.9.23",
-    "idb": "^8.0.3"
+    "idb": "^8.0.3",
+    "pixi-viewport": "^6.0.3",
+    "pixi.js": "^8.18.1"
   },
   "devDependencies": {
     "@bufbuild/protobuf": "^2.12.0",