Drop agent tooling files and neutralise spec references

- Removed CLAUDE.md, AGENTS.md and NEXTJS_REBUILD_SUPERPROMPT.md, and
  untracked .claude/ (now ignored locally via .git/info/exclude rather than
  .gitignore, so the repo carries no reference to it either).
- The Next.js 16 warning that lived in AGENTS.md is kept where it is
  actually useful, in the README tech-stack section.
- Source and migration comments referred to "the consolidation master
  prompt" and "NEXTJS_REBUILD_SUPERPROMPT.md" by name; both now read "spec",
  keeping the section numbers that made the cross-references worth having.
- README no longer lists Playwright, which is not installed, and now
  describes the three test layers that actually exist.

.gitignore

@@ -50,13 +50,6 @@ next-env.d.ts
 # hand-written lib/supabase/types.ts — never itself imported
 /lib/supabase/types.generated.ts
 
-# per-machine (permission allowlists) and must stay out of the repo
-
-# playwright
-/playwright-report
-/test-results
-/blob-report
-
 # local scratch scripts/screenshots (ad-hoc verification against a real or
 # seeded DB — can carry HR data or use SUPABASE_SERVICE_ROLE_KEY; never commit)
 .scratch_*