feat(arcade): migrate backend from NestJS to Hono/Bun

Replace @arcade/backend (NestJS) with @arcade/server (Hono/Bun).
Same two endpoints, no auth required (public game generator):
- POST /api/games/generate — AI game generation (Gemini, Claude, GPT)
- POST /api/games/submit  — Community game submission via GitHub PR
- GET  /health            — Health check

This removes the last remaining NestJS backend from the monorepo.
NestJS is now completely gone — all servers use Hono + Bun.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

games/arcade/apps/server/tsconfig.json

@@ -0,0 +1,15 @@
+{
+	"compilerOptions": {
+		"lib": ["ESNext"],
+		"target": "ESNext",
+		"module": "ESNext",
+		"moduleDetection": "force",
+		"jsx": "react-jsx",
+		"allowImportingTsExtensions": true,
+		"moduleResolution": "bundler",
+		"verbatimModuleSyntax": true,
+		"strict": true,
+		"skipLibCheck": true,
+		"noEmit": true
+	}
+}