refactor: remove eval harness module (moved to dev/)

The persona evaluation harness has been relocated to dev/ for
iterative development. Remove the eval package, CLI command,
tests, autoresearch workflow, and helper scripts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: NetDevAutomate

.github/workflows/autoresearch.yml

@@ -55,8 +55,6 @@
         # _backup.py — backup and restore user data
         "backup": "studyctl.cli._backup:backup",
         "restore": "studyctl.cli._backup:restore",
-        # _eval.py — persona evaluation harness
-        "eval": "studyctl.cli._eval:eval_group",
     },
 )
 @click.version_option()