feat(docs): Improve .env.example clarity and setup guidance for self-hosting beginners

[sebastien-lenard]

Is your feature request related to a problem? Please describe.
The current apps/web/.env.example file, while functional, can be challenging for new contributors to understand fully. It lacks explicit guidance on which variables are mandatory, where to obtain values (e.g., Supabase, Upstash, Google Cloud Console), and notes on common setup pitfalls.

Describe the solution you'd like
I've updated the apps/web/.env.example file to include:

• Clear sections for different configurations (Database, Auth, LLM, etc.).
• Labels for MANDATORY vs. OPTIONAL variables.
• Concise comments explaining the purpose of each variable.
• Hints on where to obtain API keys/credentials (e.g., "Get from Upstash.com").
• Specific notes on common setup issues (e.g., AUTH_TRUST_HOST, NEXT_PUBLIC_POSTHOG_ONBOARDING_SURVEY_ID redirect loop).

This aims to significantly improve the onboarding experience for new developers.

Describe alternatives you've considered
N/A - This is a direct improvement to existing documentation.

Additional context
I've already implemented these changes locally and verified the app runs with the new .env.example structure. I'm ready to open a Pull Request once this approach is confirmed.

[sebastien-lenard]

Test update:
I have some issues of infinite redirection caused by the onboarding process. Working on it

[elie222]

Test update: I have some issues of infinite redirection caused by the onboarding process. Working on it

do you know how to reproduce it?

[sebastien-lenard]

Yes, it's systematic after login, it loads the assistant?onboarding=true page and redirects on it continuously.
I'll find a way to figure it out, and if not will come back to you.