docs: remove legacy Claude and OpenSpec repository artifacts

[LeXwDeX]

Why

This repository no longer keeps Claude-specific or OpenSpec repository artifacts. The root CLAUDE.md deletion is intentional and must be delivered and reviewed with the current repair wave rather than restored or treated as accidental worktree damage. The current Git index contains no tracked OpenSpec-named path, so the delivery must verify that absence instead of inventing a deletion.

Scope

Delete the tracked root CLAUDE.md and verify that no tracked OpenSpec workspace/config artifact remains. Include only the intentional non-code repository artifact cleanup. Do not remove runtime compatibility behavior, source code, tests, or historical prose references merely because they mention Claude or OpenSpec.

Acceptance criteria

• Root CLAUDE.md is removed in a dedicated delivery.
• git ls-files confirms no tracked OpenSpec workspace/config artifact remains.
• Runtime code, tests, CI policy, generated files, and unrelated documentation are unchanged.
• Repository instruction discovery still uses the retained AGENTS.md hierarchy.
• Required PR checks pass and specgit finish --json exits 0.

Blocked by

• chore: sync main to dev before repair wave #476, because repair branches start only after main is synchronized into dev.

[LeXwDeX]

Delivered by PR #480 (merged into dev 2026-09-01, Closes #477). Verified: no root CLAUDE.md tracked on origin/main and no tracked OpenSpec-named paths remain. Auto-close did not fire because the merge target was dev, not the default branch.