feat: implement core pixel canvas with real-time updates

Next.js App Router + Upstash Redis BITFIELD for 2048x2048 canvas.
- 32-color palette (5-bit encoding) from rplace.live
- Batch pixel placement API (up to 256 pixels per request)
- Stackable credit rate limiting via Redis Lua script
- SSE real-time broadcasting via Redis sorted set
- HTML5 Canvas frontend with zoom/pan and color picker

package.json

@@ -0,0 +1,21 @@
+{
+  "name": "rplace-init",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint"
+  },
+  "dependencies": {
+    "@upstash/redis": "^1.37.0",
+    "next": "16.2.4",
+    "react": "19.2.4",
+    "react-dom": "19.2.4"
+  },
+  "devDependencies": {
+    "eslint": "^9",
+    "eslint-config-next": "16.2.4"
+  }
+}