consolidation: add RATIONALIZATION-PENDING README banner (blocks until R1)

[Delqhi]

Add RATIONALIZATION-PENDING banner to README

Tracker: OpenSIN-overview/docs/FOLLOWUPS.md § R1

Why

This repo is flagged rationalization-pending in the April 2026 org consolidation. It overlaps with the canonical OpenSIN-AI/OpenSIN-Code (see CANONICAL-REPOS.md § 9). Until the decision in R1 lands, new features must not be added here — otherwise the eventual merge/split gets harder every week.

Acceptance criteria

• Add the following banner to the top of README.md, above the existing content:

  > ## ⚠️ RATIONALIZATION PENDING
  >
  > This repository overlaps with the canonical [`OpenSIN-AI/OpenSIN-Code`](https://github.com/OpenSIN-AI/OpenSIN-Code) and will either be merged into it or narrowed to "Rust engine only" — decision tracked in [OpenSIN-overview § R1](https://github.com/OpenSIN-AI/OpenSIN-overview/blob/main/docs/FOLLOWUPS.md#r1-opensin-ai-cli--opensin-code).
  >
  > **Do not extend this repository** until R1 is resolved. New coding-CLI work belongs in `OpenSIN-Code`.

• Replace any reference to the archived OpenSIN-AI/opensin-ai-code with OpenSIN-AI/OpenSIN (consolidated there in Wave 1)
• Close this issue when R1 is resolved (banner can then be removed together with the flag)

[Delqhi]

Wave 4 update — consolidation-ticket owners please read

Context from the overview repo on 2026-04-19 (commits on PR overview#46):

• L1 (Delqhi link sweep) is DONE. Live gh search code turned up 0 actionable hits org-wide. The sweep assumption was wrong; reality cleared itself.
• L2 (archived-repo refs) has live evidence: 26 hits for A2A-SIN-Coding-CEO, 1 for OpenSIN-onboarding. Procedure in FOLLOWUPS § L2.
• M2 (oh-my-sin aggregator) is partial-done. templates/oh-my-sin.json is now the SSOT. 17 teams, 87 agents referenced. The proposed nightly workflow installs via install.sh.
• S2 (6 A2A-SIN-Code- scaffolds)* audit complete in docs/S2-DEAD-REPO-AUDIT.md. Decision matrix is gated by this R1 ticket.

Decision deadline: 2026-04-22 18:00 CET

If R1 is not resolved by that time, the S2 fallback (collapse 6 scaffolds to 1) auto-applies so T-0 has a clean story. No launch is blocked by R1 itself — but keeping it undecided forces a worse S2 branch.

Reference graph

• Launch plan: LAUNCH-CHECKLIST.md
• Command Center issue: overview#47
• CEO directive: overview#40
• Waiver log: governance/WAIVER-LOG.md