245. Indexer origin-only error logging

Motivation

ERD_INDEXERS_CHECKLIST.md still leaves the origin-only error logging rules unchecked even though the indexer stack already carries structured code and sqlstate fields through typed errors.
crates/revaer-app/src/indexers.rs was re-logging propagated DataError values while also converting them into service errors, which duplicated origin logs and violated AGENTS.md.
The next efficient step is to make the app-layer mapper functions pure translations so origin logs remain singular while callers still receive stable service error kinds and structured context.

Remove tracing::error! side effects from the indexer service error-mapper helpers in crates/revaer-app/src/indexers.rs.
Keep the existing mapping taxonomy unchanged so service callers still receive the same kind, code, and sqlstate values.
Add mapper coverage proving structured error context survives translation without requiring logging side effects.

Added a unit test covering representative mapper paths for definition, tag, and indexer-field errors.
The new assertions verify kind, code, and sqlstate preservation for propagated stored-procedure failures.
Full repository quality gates remain the final verification for regression safety.

No new emitters were added.
This change reduces duplicate logs by keeping error emission at the actual failure origin while preserving structured context on returned service errors.

Risk is low because the change is limited to log side effects in app-layer error translation.
If diagnostics regress, rollback is a straight revert of the mapper cleanup and accompanying checklist/task-record updates.