--report FILE on check and fix writes the findings a run already
computed into CI-consumable formats chosen by extension: .sarif
(single run, %SRCROOT%-relative URIs, properties.autoFixable, rule
registry with descriptions) and .xml (Checkstyle, source=jmove.<rule>).
Unknown suffixes fail fast with INVALID_ARGUMENT; stdout and exit codes
are untouched, and clean runs write valid empty documents.
The check handler moved into cli::report (its format siblings); fix
emits the candidate list in dry-run and apply modes. Marketing angle
from the plan: auto-fix for what Checkstyle only reports.
