ExecuteSpec setup: contract index and codemap for navneetprabhakar/executor

[navneetprabhakar]

Initial .executespec/ folder seeded by ExecuteSpec at link time. See .executespec/README.md for what each subfolder is for and which paths are regenerable vs review-worthy.

What happens after you merge this?

• You don't need to sync. ExecuteSpec watches the GitHub webhook — when this PR merges, the project dashboard automatically flips this repo from 'Bootstrap PR open' to 'Bootstrapped'. No manual click required.
• No duplicate bootstrap PRs. If something later re-triggers the bootstrap path (e.g. an admin re-runs /api/admin/projects/{id}/migrate-codemaps), ExecuteSpec sees .executespec/README.md already on the default branch and short-circuits to BOOTSTRAPPED instead of opening a second PR.
• Architecture / codemap PRs. Once you click Analyse on the project (or the chat tool regenerate_architecture fires), ExecuteSpec writes per-repo codemaps + an architecture doc to .executespec/arch/. Those land as their own PRs (kind=ARCHITECTURE in the dashboard rollup) and only re-open when source code actually changes — the writer compares content hashes and skips empty PRs.
• New repos joining this project. Linking another repo to the project triggers exactly one bootstrap PR for that repo. This repo's bootstrap state is untouched.