fix(update): don't crash hermes update if skill config scan fails (#18257)

`hermes update` ran the config migration (11 → 17) successfully then
crashed at `agent/skill_utils.py:340` during the post-migration
skill-config prompt. User @FlockonUS reported this on Twitter.

Root cause: `get_missing_skill_config_vars` in hermes_cli/config.py
only guarded the import of `discover_all_skill_config_vars`, not the
call. Any runtime exception inside the skill scan (malformed SKILL.md,
unreadable external skill dir, etc.) propagated up through
`migrate_config` and aborted `hermes update` after the version bump.

Wrap the call in try/except so skill-config prompting — which is a
post-migration nicety — can never block the migration itself.

hermes_cli/config.py

@@ -2437,7 +2437,17 @@ def get_missing_skill_config_vars() -> List[Dict[str, Any]]:
     except Exception:
         return []
 
-    all_vars = discover_all_skill_config_vars()
+    try:
+        all_vars = discover_all_skill_config_vars()
+    except Exception as e:
+        # A malformed SKILL.md, unreadable external skill dir, or similar
+        # should never break `hermes update`.  Skill-config prompting is a
+        # post-migration nicety, not a blocker.
+        import logging
+        logging.getLogger(__name__).debug(
+            "discover_all_skill_config_vars failed: %s", e
+        )
+        return []
     if not all_vars:
         return []