Document repo split, desktop API URL, and env template

[Copilot]

Summary

Clarify that this repo is the web/server app, document the companion Electron repo and recommended shared root structure, and add a standard .env.example with the required runtime variables.

Related issue

Changes

• Docs: repo layout & desktop API URL — explain the web/server vs desktop repos, recommended folder layout, and how to set VITE_API_URL for hosted and local use.
• Docs: environment variables — align README env section with the required variables and point to .env.example.
• Contributing guidance — ask contributors to open discussions before large features to align scope with maintainers.

Example snippet:

IMAGEKIT_PRIVATE_KEY=
IMAGEKIT_PUBLIC_KEY=
IMAGEKIT_URL_ENDPOINT=
MONGODB_URI=
NEXT_PUBLIC_URL=https://callu.up.railway.app
OTP_BCC_EMAIL=
PORT=
RESEND_API_KEY=
RESEND_FROM_EMAIL=

Testing

• Not requested (documentation and template changes only)

Checklist

• Title follows the repository PR format
• The issue is linked with Fixes #<issue-number>
• Testing notes are included

[Copilot]

Pull request overview

This PR is documentation-only: it updates the README to clarify that this repo is the web/server app, points to a companion Electron repo, documents how to configure the desktop app's VITE_API_URL, simplifies the environment variable section to point at a new .env.example, and adds contributor guidance to open a discussion before large features.

Changes:

• Adds a "Repositories & Sync" section explaining the web/server vs desktop repos and recommended folder layout.
• Replaces the inline annotated env block with a condensed list aligned to .env.example and adds a local-dev note.
• Updates Contributing section to request a prior discussion for large features.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.