config: adopt version.minimum_library_version floor (2026.7.9.1)

Phase 4 task 1 (PyAutoBuild#155). Move the compatibility floor to the canonical
version.minimum_library_version key autoconf prefers over legacy
workspace_version. Behavioural no-op: both resolve to 2026.7.9.1 (first
post-redesign INSTALLABLE release; 2026.6.x-2026.7.6.649 are yanked).
workspace_version kept until the version_skew rework reads it.

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

Author: 2 people

config/general.yaml

@@ -49,5 +49,11 @@ test:
   lh_timeout_seconds:               # If a float is input, the log_likelihood_function call is timed out after this many seconds, to diagnose infinite loops. Default is None, meaning no timeout.
   disable_positions_lh_inversion_check: true
 version:
+  # The compatibility FLOOR: the oldest library release whose API this
+  # workspace's scripts require. Preferred over workspace_version
+  # (autoconf/workspace.py). Bump DELIBERATELY — only when a script
+  # 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.