chore: remove temporary plan files that were accidentally merged

[eunjae-lee]

What does this PR do?

Removes two temporary implementation plan files that were accidentally merged into the repository:

• packages/features/feature-opt-in/FEATURE_OPT_IN_BANNER_PLAN.md — Feature opt-in banner system plan
• packages/features/flags/DECORATOR_IMPLEMENTATION_PLAN.md — Memoize/Unmemoize decorator implementation plan

These are internal planning documents, not project documentation, and should not live in the codebase.

No functional code changes.

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A
• I confirm automated tests are in place that prove my fix is effective or that my feature works. N/A — deletion of non-code files only.

How should this be tested?

No testing needed — this PR only deletes markdown plan files. Verify the two files no longer exist after merge.

Human Review Checklist

• Confirm no other temporary plan files remain in the repo (I searched for *PLAN*.md and only found these two)
• Verify these files are not referenced or linked from any code or docs

---

Requested by: @eunjae-lee
Link to Devin session: https://app.devin.ai/sessions/48e0b613eea64389811af91c09910bd3

[devin-ai-integration]

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[cubic-dev-ai]

No issues found across 2 files

[paragon-review]

Paragon: tests updated

1 new test generated for this PR.

New Tests

• no-plan-files.test —

Details

New Tests

• no-plan-files.test (unit)