Fixes typing issues and null check in github workflow

[arii]

• Fixed any cast with proper typescript intersection type in scripts/gemini-client.ts.
• Replaced a [ -n "$REVIEW_COMMENT" ] with an explicit check for the literal string "null" [[ -n "$REVIEW_COMMENT" && "$REVIEW_COMMENT" != "null" ]] in .github/workflows/reusable-gemini-review.yml.

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PR created automatically by Jules for task 2904124573259627833 started by @arii

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[github-actions]

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