chore: upgrade runtime to Bun 1.4.0

- Update Nix flake.nix overlay to use Bun 1.4.0 (overrideAttrs)
- Update CI (setup-bun) to pin bun-version: 1.4.0
- Update package.json packageManager/Dockerfile/vercel.json
- sha256: sha256:Poy0vf7yJ/hzk33QiQj5gnshI5Q7dfbaMD7xgwiyDKw=

Dockerfile

@@ -1,4 +1,4 @@
-FROM oven/bun:1.3-alpine
+FROM oven/bun:1.4-alpine
 WORKDIR /app
 
 # Install curl for IPv6 source rotation

README.md

@@ -369,7 +369,7 @@ PORT=4090 CACHE_TTL=600000 bun src/index.ts
 - **Docker**:
 
   ```dockerfile
-  FROM oven/bun:latest
+  FROM oven/bun:1.4-alpine
   WORKDIR /app
   COPY package.json bun.lock .
   RUN bun install

vercel.json

@@ -1,6 +1,6 @@
 {
   "framework": null,
-  "bunVersion": "1.x",
+  "bunVersion": "1.4.0",
   "rewrites": [
     { "source": "/(.*)", "destination": "/api/relay" }
   ]