Refresh token validate expires_at

[askmy-stack]

Background

Identified during OSS audit v2 of startupintel.

Problem Statement

Expired tokens may rotate.

Proposed Solution

Check expires_at.

Acceptance Criteria

• Implementation complete
• Tests pass
• Documented in README or docs/

Files / Modules Affected

startupintel/api/routes/auth.py

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Suggested labels: priority:medium, difficulty:beginner, category:security
Milestone: v2.0-features
OSS Audit: Master Backlog v2