chore(rtk): AGENTS.md as the shared instruction file, project rtk filters

[mhenrixon]

Summary

• Moved the full root CLAUDE.md body into AGENTS.md, the single project-instruction file
  shared across Claude Code, Grok, Cursor, Copilot and Codex. No rule content was dropped or
  changed, only relocated and given a short intro.
• CLAUDE.md is now a stub that @-imports AGENTS.md, matching the getzazu/app#4104 pattern.
• No merge was needed (AGENTS.md didn't exist yet) and no other file referenced CLAUDE.md as
  "the project rules" — pgmq-ruby.gemspec's spec.files list never shipped CLAUDE.md in the
  gem package, so nothing to fix there either. No .github/copilot-instructions.md or
  .gitattributes in this repo.
• Added .rtk/filters.toml for the two commands that are genuinely noisy and not already handled
  by the global rtk hook:
  • rake test — Postgres/PGMQ NOTICE: chatter interleaved into the Minitest dot-progress line,
    plus 4 recurring SimpleCov.add_filter deprecation lines. Verified live: 43 → 8 lines
    (rtk bundle exec rake test, exit code unchanged at 0, 267 runs, 625 assertions, 0 failures
    preserved).
  • bin/integrations — decorative ==== banners, Example: <name> titles, and per-spec
    Cleaning up N queue(s)... / Dropped: ... chatter repeated once per integration spec.
    Verified live: 405 → 140 lines (rtk bin/integrations, exit code unchanged at 0, the
    final All 19 integration spec(s) passed. line preserved).
  • Both filters were rtk trust --yes + rtk verify'd (158/158 inline tests pass, including
    the 5 I added, built from real captured output).
• Skipped filters for:
  • bundle exec rubocop and bundle exec yard-lint lib/ — already rewritten/clean (rubocop
    is in the global hook's known-command list; yard-lint prints a single No offenses found
    line on a clean run, nothing to strip).
  • docker compose up -d and npm ci — not rewritten by the hook, but their real output is
    already short (3 and 9 lines respectively) and not noisy enough to justify a filter.
  • npx lostconf --fail-on-stale — already rewritten by the global hook.
  • zazu's brakeman / lingo / rails db:* filters were not copied — this repo runs none of
    those commands.
• No bin/setup (or equivalent) exists in this repo, so no new idempotent rtk trust --yes setup
  step was added.
• Added a short rtk note to AGENTS.md's Testing section naming the two filtered commands.
• No screenshots section — this is a CLI-only Ruby gem with no UI/dashboard/rendered output.

Adopts getzazu/app#4104.

Test plan

• rtk trust --yes + rtk verify — 158/158 inline tests pass
• rtk hook check "bundle exec rake test" / "bin/integrations" — both now show the project
  filter's rewrite
• Live end-to-end run of both filtered commands against a real docker compose up -d Postgres
  + PGMQ extension instance — line-count reduction confirmed, exit codes and pass/fail counts
  unchanged
• grep -rn "CLAUDE.md" across the repo (excluding .git) — only the intentional
  self-reference inside AGENTS.md remains
• Full bundle exec rake test / bin/integrations — not run as CI (docs/config-only change);
  spot-verified above instead

---

Summary by cubic

Consolidates project instructions into AGENTS.md so Claude Code, Grok, Cursor, Copilot, and Codex all read the same file; CLAUDE.md is now a stub that imports AGENTS.md, with no rule content changed. Adds .rtk/filters.toml to strip noisy output from rake test and bin/integrations—Postgres/PGMQ NOTICE: lines, SimpleCov deprecation warnings, and per-spec banners/cleanup chatter—while preserving exit codes and pass/fail summaries. The Testing section in AGENTS.md now documents that edits to .rtk/filters.toml require rtk trust --yes and rtk verify.

^{Written for commit 8afdff2. Summary will update on new commits.}