docs: remove obsolete implementation tracker

[leaanthony]

Summary

• remove the root IMPLEMENTATION.md tracker
• remove its exception and GTK maintenance requirements from AGENTS.md
• keep GitHub issues and pull requests as the single authoritative implementation tracker

Why

The root tracker duplicates project state already maintained in GitHub and caused unrelated documentation churn and merge conflicts on #5972. Removing the file and its agent instructions prevents future work from recreating that scope expansion.

Historical tracker content remains available through Git history. The existing reference under history/ is intentionally left as an archival artifact.

Validation

• git diff --check
• searched the repository for live IMPLEMENTATION.md instructions; only the archival history/beta-readiness-audit.html reference remains
• attempted the required CodeRabbit review; the free OSS review quota was exhausted

Summary by CodeRabbit

• Documentation
  • Removed the obsolete implementation-tracking document covering Linux support, architecture, compatibility, packaging, testing, and known limitations.
  • Updated project guidance to classify AI planning documents as temporary files stored in the history directory.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 922a8311-cc6a-4566-bf69-c0e170a30976

📥 Commits

Reviewing files that changed from the base of the PR and between 2ba81ba and 4cc1255.

📒 Files selected for processing (2)

• AGENTS.md
• IMPLEMENTATION.md

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Walkthrough

The change updates AGENTS.md to store listed AI planning documents under history/. It adds PLAN.md to the list, removes the root IMPLEMENTATION.md exception, and deletes IMPLEMENTATION.md.

Changes

Planning document policy

Layer / File(s)	Summary
Ephemeral planning document guidance AGENTS.md, IMPLEMENTATION.md	AGENTS.md now requires listed planning documents to reside in history/, includes PLAN.md, and removes the root IMPLEMENTATION.md exception. IMPLEMENTATION.md is deleted.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Poem

A rabbit files plans in a history burrow,
With PLAN.md tucked away from tomorrow.
The root guide is clear,
Old tracking disappears,
And tidy paths make the carrots grow.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/remove-implementation-tracker

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[Copilot]

Pull request overview

Removes the now-obsolete root-level IMPLEMENTATION.md implementation tracker and updates agent guidance to keep GitHub Issues/PRs as the single source of truth for implementation tracking, reducing documentation churn and merge conflicts.

Changes:

• Delete the root IMPLEMENTATION.md tracker document.
• Remove the special-case exception and maintenance requirements for that tracker from AGENTS.md.
• Keep archival historical references under history/ (no live repo references remain).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
IMPLEMENTATION.md	Removed obsolete root implementation tracking document (historical content remains in Git history).
AGENTS.md	Updated agent instructions to remove the IMPLEMENTATION.md exception and related maintenance requirements.

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