Drop legacy workspace_version + version.txt

Mirror the already-merged version-model-honesty work (6 other workspaces)
on canonical HowToFit: remove `version.workspace_version` from
config/general.yaml and delete version.txt. The compatibility floor
(minimum_library_version) and workspace_version_check remain.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 2 people

config/general.yaml

@@ -37,5 +37,4 @@ version:
   # starts needing new API — never per release. Must always name an
   # INSTALLABLE (non-yanked) release.
   minimum_library_version: 2026.7.9.1
-  workspace_version: 2026.7.9.1
   workspace_version_check: True     # If False, bypass the workspace/library version check. Set to False on `main`-branch clones — `main` updates faster than releases, so mismatches are expected and not actionable.