Document Render free-tier semantic search limitations

[askmy-stack]

Background

Identified during OSS audit v2 of cortex.

Problem Statement

render.yaml disables semantic.

Proposed Solution

Explicit limitations in DEPLOY-FREE.md.

Acceptance Criteria

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

Files / Modules Affected

render.yaml, docs/DEPLOY-FREE.md

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