docs: clarify WebSocket package usage for Node.js vs browser environments

[Rohan170603]

Problem

The local development guide contains ambiguous comments about the ws package. The Database Branching section implies Node.js lacks WebSocket support, while the Local PostgreSQL section imports ws without explanation. This causes confusion around when the package is actually required.

Solution

• Updated comments in Database Branching to clarify: Node.js requires ws package, browsers/Edge have native WebSocket support
• Added explanatory comment to all three Local PostgreSQL tabs (neondatabase/serverless, Drizzle, Prisma)

Impact

• Prevents "WebSocket is not defined" errors in Node.js
• Avoids unnecessary ws installation in browser environments
• Aligns with official Neon and Drizzle documentation

[vercel]

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