Move the BLOCKER/WARNING/INFO conflict report format, severity semantics,
and safety-gate behavior from workflows/import.md into a new shared
reference file. /gsd-import consumes the reference; behavior is unchanged
(all 13 import-command tests + full 4091-test suite pass).
Prepares for /gsd-ingest-docs (#2387) which will consume the same contract
with its own domain-specific check list. Prevents drift between the two
implementations.
Refs #2387
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>