Add Environment Variable Validation

[Abd-Standard]

Description

Validate required environment variables during application startup.

Tasks
Check required variables.
Display descriptive errors.
Prevent startup when configuration is invalid.

Acceptance Criteria
Missing variables produce meaningful error messages.
Application exits safely when configuration is incomplete.

[squad0011]

Hey Maintainer, I would love to take on this issue to implement strict environment variable validation at application startup. Failing fast with clear error messages prevents unpredictable runtime crashes later on.

[grantfox-oss]

🦊 GrantFox — @squad0011 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #5)
2. Your PR will be reviewed by the Core-Foundry maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@squad0011's PR #59 was approved and merged by @Abd-Standard.

🏆 @squad0011: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (48 total points). Track your full progress on GrantFox.

👏 Great work, @squad0011! Keep contributing to Core-Foundry.