Document canonical dependency install path

[askmy-stack]

Background

Identified during OSS audit v2 of meridian.

Problem Statement

uv vs requirements unclear.

Proposed Solution

Single documented path.

Acceptance Criteria

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

Files / Modules Affected

README.md

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Suggested labels: priority:medium, difficulty:beginner, category:documentation
Milestone: v1.0-oss-ready
OSS Audit: Master Backlog v2