fix: guard /api/ai/roast against missing GEMINI_API_KEY

[vipul674]

Summary

The /api/ai/roast route created the GoogleGenerativeAI client at module level with an empty key, so calls threw a cryptic Google SDK error as a 500. Guard the key and return a clear error, and document GEMINI_API_KEY in .env.example.

Closes #3109

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

What Changed

• Guard in src/app/api/ai/roast/route.ts returning 500 with a clear message when GEMINI_API_KEY is missing
• GEMINI_API_KEY documented in .env.example

[github-actions]

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[Copilot]

🟡 Not ready to approve

The Gemini client is still constructed at module load time with an empty-string key, which can fail before the request-level guard executes and should be refactored to lazy initialization after validating GEMINI_API_KEY.

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Pull request overview

This PR aims to make the /api/ai/roast endpoint fail gracefully when GEMINI_API_KEY is not set, instead of surfacing a cryptic upstream Google SDK error, and documents the required env var for contributors/self-hosters.

Changes:

• Adds a missing-GEMINI_API_KEY guard in src/app/api/ai/roast/route.ts to return a clear JSON error response.
• Documents GEMINI_API_KEY in .env.example with usage context for the /api/ai/roast route.

File summaries

File	Description
src/app/api/ai/roast/route.ts	Adds an env-var guard to prevent calling Gemini without credentials and returns a clearer error response.
.env.example	Adds documentation for GEMINI_API_KEY so the roast route can be configured correctly.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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[vipul674]

👋 @Priyanshu-byte-coder — PR is ready for review. Please take a look when you get a chance. Thanks!