feat: add standalone Checkstyle linting

[zeitlinger]

Blocked by #447

Summary

• add standalone Checkstyle support using the curated JAR and Java runtime
• treat Checkstyle warning/error output as a failed check
• add generated documentation, tool pins, and focused end-to-end cases

Split from #430 so the Checkstyle integration can be reviewed independently.

Validation

• mise run generate
• mise run lint:fix
• mise exec -- cargo test

[zeitlinger]

Pre-release consumer validation is running in prometheus/client_java#2341.

The standalone all-files run initially found 165 warnings: 160 in test sources, one archived benchmark warning, and four example-source warnings. The consumer PR preserves client_java's existing Maven Checkstyle scope with narrow suppressions; flint run --full checkstyle, mise run lint:fix, and the full Maven build pass locally.

[zeitlinger]

Checkstyle now uses the Aqua package from aquaproj/aqua-registry#57625. Current Flint CI failures are expected until that package is merged into the registry; the package PR is mergeable and all checks are green.

[zeitlinger]

CI is currently waiting for the next mise release: the Checkstyle package was merged into aqua-registry in aquaproj/aqua-registry#57625, but mise v2026.7.13 still bundles an older Aqua registry snapshot.

[Copilot]

Pull request overview

This PR adds first-class, standalone Checkstyle support to Flint by registering a new checkstyle check (invoked via java -jar), treating warning/error markers as failures even when the process exits 0, and rounding out the integration with docs, tool pins, and focused end-to-end fixture cases.

Changes:

• Add checkstyle to the built-in registry with baseline config expectations and failure-on-output markers ([WARN], [ERROR]).
• Extend the runner/command spawning to support java -jar invocation and failing checks based on output patterns (stdout/stderr).
• Add Checkstyle e2e cases plus generated docs and dependency/workflow pin updates.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/cases/checkstyle/warning/test.toml	New e2e case asserting warning output causes a failed check
tests/cases/checkstyle/warning/files/mise.toml	Fixture tool pin for Checkstyle
tests/cases/checkstyle/warning/files/Foo.java	Java fixture input
tests/cases/checkstyle/warning/files/checkstyle.xml	Minimal Checkstyle config fixture
tests/cases/checkstyle/missing-config/test.toml	New e2e case for missing checkstyle.xml behavior
tests/cases/checkstyle/missing-config/files/mise.toml	Fixture tool pin for Checkstyle
tests/cases/checkstyle/missing-config/files/Foo.java	Java fixture input
tests/cases/checkstyle/clean/test.toml	New e2e case for clean Checkstyle run
tests/cases/checkstyle/clean/files/mise.toml	Fixture tool pin for Checkstyle
tests/cases/checkstyle/clean/files/Foo.java	Java fixture input
tests/cases/checkstyle/clean/files/checkstyle.xml	Minimal Checkstyle config fixture
src/runner.rs	Add failure_output_patterns support and output scanning helper
src/registry/types.rs	Introduce JavaJarMode + failure-output-patterns on Check
src/registry/checks.rs	Register the new checkstyle check and its configuration
src/main.rs	Update expected linter table output to include Checkstyle
src/linters/mod.rs	Generalize JAR spawning to support java -jar (incl. non-Windows)
src/init/scaffold.rs	Bump pinned mise version/hash in generated scaffold
README.md	Add Checkstyle to the Java linter row in the top-level table
mise.toml	Pin Checkstyle and adjust Renovate pin with trust-policy excludes
docs/linters/checkstyle.md	New generated linter documentation page
docs/linters.md	Add Checkstyle to the linter index table
default.json	Add checkstyle to default tool enablement list
.github/workflows/test.yml	Bump pinned mise version/hash in CI matrix
.github/workflows/release.yml	Bump pinned mise version/hash in release workflow
.github/workflows/release-plz.yml	Bump pinned mise version/hash in release-plz workflow
.github/workflows/mise-registry.yml	Bump pinned mise version/hash in mise-registry workflow
.github/workflows/lint.yml	Bump pinned mise version/hash in lint workflow
.github/renovate.json5	Track Checkstyle in Renovate-managed tool list
.github/renovate-tracked-deps.json	Add Checkstyle datasource mapping and tracked tool list entry

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