feat(skills): cloud sync client + incremental sync + fork-on-revocation

Adds CloudApiSkillClient (Cloud API per-host sync endpoint + inventory
report), forwards since_version for incremental sync (full-replace on
first/stale), and forks a local override into a standalone local skill
when its cloud skill is revoked (design D9). Skill-side tests green (87
passed).

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

storage/skill_catalog.py

@@ -143,6 +143,18 @@ class SkillCatalogStore:
                 (subscription_id, 1 if active else 0),
             )
 
+    def _get_subscription_version(self, subscription_id: str) -> int | None:
+        """Last successfully applied ``latest_version`` for a subscription."""
+        with self._connect() as conn:
+            row = conn.execute(
+                "SELECT last_synced_version FROM subscriptions WHERE id = ?",
+                (subscription_id,),
+            ).fetchone()
+        if row is None:
+            return None
+        value = row["last_synced_version"]
+        return int(value) if value is not None else None
+
     def _set_subscription_state(
         self,
         subscription_id: str,