Two small follow-ups to the faststream 0.7 migration (PRs #3, #4):

1. Narrow uv_build's upper bound from <1.0 to <0.12, matching upstream's
   stated versioning policy (the 0.x component is where breaking changes
   ship, not the major). Floor moves from 0.11 to 0.11.18 — the release
   where uv_build was stabilized. Same posture the migration just
   adopted for faststream: bound on both sides.

2. Add one-line rationale comments above the two retained
   '# ty: ignore[invalid-argument-type]' sites in main.py. Both
   ignores were re-verified during PR2 (ty still fires the error on
   0.7.1 if removed). The WHY is non-obvious — both stem from upstream
   structural type frictions that can't be solved at this layer —
   so a future contributor should not optimistically delete them
   without understanding the constraint.

No behavior change. lint + tests green at 100% coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

uv_build is a build-time dependency — [build-system].requires only
affects whoever runs `uv build`, not downstream installers. A breaking
uv_build 0.12 surfaces as a single failing build, recoverable in one
commit at that time. Tightening preemptively just creates churn at
every minor bump with no user-facing protection in exchange.

PR #5 now ships annotations-only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

chore: annotate retained ty:ignore comments in middleware

- Bump pins: checkout@v4 → @v6, setup-just@v2 → @v4, setup-uv@v3 → @v8.2.0
  across ci.yml and publish.yml.
- Drop codecov upload step from ci.yml. Coverage floor enforced by
  --cov-fail-under in pyproject.toml; modern-di also dropped codecov.
- Split ci.yml into thin trigger wrapper + reusable _checks.yml
  (workflow_call). Sets the shape up to add more callers later.

Resulting ci.yml/_checks.yml/publish.yml are byte-identical to
lite-bootstrap's post-PR #115 state.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

modern-di's docs moved from Read the Docs to GitHub Pages
(modern-di.modern-python.org). Updates the docs URL in pyproject.toml
and the Documentation link in README.md to match.

ci: align with modern-di