[FEATURE] Deprecate implemented plans or move them to /plans/archive

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

All the new /plans features are great, only there are sometimes unnecessary re-reads that happen when Claude tries to determine whether or not to build on or move on from a previously implemented plan. Wastes tokens and time.

Proposed Solution

Move implemented plans to /plans/archive.
Establish /plans/index.json (where each plan gets a natural language summary).

Alternative Solutions

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Priority

High - Significant impact on productivity

Feature Category

File operations

Use Case Example

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Additional Context

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