feat(rules): a rule keeps what it used to say — rule_versions (#3240, milestone 323 step 1)

The sibling notes already had. `note_versions` snapshots a note's every
meaningful edit; a RULE, which binds behaviour on every session that loads
it, had nothing — an edit destroyed the previous wording with no record
anywhere. Rescoping rule 79 meant hand-copying the superseded statement into
a task log to keep it (#3237). The more consequential record had the weaker
protection.

Schema and transport only. Nothing writes a version yet — that is step 2.

Three guards are deliberately NOT copied from note_versions, each defending
against autosave, which rules do not have: no pruning or MAX_VERSIONS, no
pin columns, no minimum interval. A rule is edited a handful of times in its
life, and capping invites losing the one edit somebody needed.

`user_id` is the ACTOR rather than the owner, and SET NULL rather than
CASCADE: deleting a user must not erase the history of the rules they
edited. The restore diverges from its NoteVersion sibling accordingly — an
unmappable user leaves the row with a null actor instead of dropping it,
which is the whole point of choosing SET NULL. The integration round trip
pins that, because nothing in the code says which of the two shapes is
intended and "make it match the sibling" would silently delete the record.

Backup goes to v13. Both export paths carry the table; the per-user one
scopes through the rule rather than the version's user_id, or it would carry
the versions this user wrote on someone else's rule and drop the ones
someone else wrote on theirs. The restore remaps rule_id through
rule_id_map — #3182's arose_from_id trap on a new table.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_services_backup.py

@@ -23,7 +23,7 @@ def test_backup_version_is_current():
 
     (Named for the number it asserted until v10, which is exactly the drift a
     name-carrying-a-value invites; it now says what it checks.)"""
-    assert backup.BACKUP_VERSION == 12
+    assert backup.BACKUP_VERSION == 13
 
 
 def _exportable_note(**over):
@@ -134,6 +134,7 @@ def _column_guard_targets():
     from scribe.models.note_supersession import NoteSupersession
     from scribe.models.note_usage import NoteUsageEvent
     from scribe.models.note_version import NoteVersion
+    from scribe.models.rule_version import RuleVersion
     from scribe.models.project import Project
     from scribe.models.repo_binding import RepoBinding
     from scribe.models.rulebook import Rule, Rulebook, RulebookTopic, RuleRelation
@@ -154,6 +155,7 @@ def _column_guard_targets():
         "rulebooks": (Rulebook, backup._rulebook_rows),
         "rulebook_topics": (RulebookTopic, backup._topic_rows),
         "rules": (Rule, backup._rule_rows),
+        "rule_versions": (RuleVersion, backup._rule_version_rows),
         "systems": (System, lambda rows: backup._system_rows(rows, {})),
         "canonical_systems": (CanonicalSystem, backup._canonical_system_rows),
         "record_systems": (RecordSystem, backup._record_system_rows),