ci: ruff check and mypy do not cover the compatibility consumer fixtures

[codeforester]

Problem

The authoritative style gate scopes ruff to four paths and excludes compatibility/
(tests/full_validate.sh:49-51):

ruff format --check lib/python/base_cli scripts examples tests
ruff check       lib/python/base_cli scripts examples tests

compatibility/consumers/ holds the three consumer fixtures — atlas_click, beacon_typer,
cinder_automation — that the project uses as its compatibility and adoption evidence, surfaced
through docs/compatibility-dashboard.md and scripts/validate_consumers.py. They are lint-exempt,
and there are real violations sitting in them today.

The typing gate has the same shape (tests/full_validate.sh:43-45): mypy --strict covers
lib/python/base_cli and the single file examples/typed_consumer.py. The example applications
under examples/*/src/** and all of compatibility/ are unchecked, even though they are the code
adopters copy.

This matters more than ordinary lint debt: these fixtures exist specifically to demonstrate what
good consumer code looks like.

Verified evidence

Reviewed 2026-09-30 at a58ec109349fa3f3d03eae5b0de078b39ea361a2.

$ ruff check .
Found 6 errors.
[*] 6 fixable with the `--fix` option.

I001 Import block is un-sorted or un-formatted
 --> compatibility/consumers/atlas_click/src/atlas_click/cli.py:3:1

All six are I001 in compatibility/consumers/**. ruff format --check compatibility passes
(13 files already formatted), so this is purely the un-run ruff check.

Proposal

1. Add compatibility to both ruff invocations in tests/full_validate.sh and fix the six I001
   violations.
2. Extend the typing gate to the example and compatibility consumer packages. If full --strict is
   not appropriate for them, run non-strict mypy and record why in the script, so the scope is a
   decision rather than an omission.
3. Consider inverting the default: lint the repository (ruff check .) and list exclusions
   explicitly, so a new top-level directory is covered by default instead of silently exempt.

Acceptance criteria

• ruff check and ruff format --check run over compatibility/ in CI and pass.
• The gate's scope is either the whole repository with explicit exclusions, or a list with a comment
  explaining each omission.
• Example and compatibility consumer packages are type-checked at a documented strictness.
• A new top-level Python directory is covered by the gates without editing the path list, or the
  script fails loudly if it is not.

Non-goals

• Do not change the ruff rule selection or line-length configuration in pyproject.toml.
• Do not reformat lib/python/base_cli.