Export route streaming for large datasets

[askmy-stack]

Background

Identified during OSS audit v2 of startupintel.

Problem Statement

Full JSON OOM.

Proposed Solution

StreamingResponse CSV.

Acceptance Criteria

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

Files / Modules Affected

startupintel/api/routes/export.py

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Suggested labels: priority:low, difficulty:intermediate, category:performance
Milestone: v2.0-features
OSS Audit: Master Backlog v2