Environment variable reference

[codebestia]

Write docs/environment-variables.md: one table of every environment variable across all four apps — name, which app reads it, required vs optional, default, and what breaks if it is wrong. Source it from apps/backend/src/config.ts, .env.example, apps/backend/src/config/rateLimits.ts, the NEXT_PUBLIC_* vars in apps/web, and the AI agent's settings.

Acceptance criteria:

• Every variable in .env.example appears, plus any read directly via process.env that .env.example omits
• Marks which variables are validated at boot by config.ts (crash on start) vs. read lazily (silent misbehaviour)
• Flags secrets explicitly and states they must never be committed
• Notes which NEXT_PUBLIC_* values are compiled into the client bundle and therefore public

[fathiaoyinloye]

@fathiaoyinloye has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I'd like to work on this issue. I have relevant experience with the technologies and concepts involved, and I'm confident I can make the necessary implementation to ensure the it meets the acceptance criteria. I'd be happy to contribute to this task.

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[KodeSage]

@KodeSage has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

please assign this issue to me.
I’d like to work on this issue because environment variables are one of those parts of a system that can look simple but have a major impact on whether an application actually works correctly.

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[github-actions]

Closed by #613, merged into dev.

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This issue has been completed by @KodeSage as part of the Stellar Wave Program's 9th Wave 🥳

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