fix(skills): apply global|platform disabled union to all resolution sites

The platform-disabled fix landed only in agent.skill_utils.get_disabled_skill_names
(the system-prompt path). Two sibling resolvers still used the old
replace-not-union semantics, so the same skill could be hidden from the
<available_skills> prompt yet reported enabled elsewhere:

- hermes_cli/skills_config.get_disabled_skills (the 'hermes skills config' UI)
  returned only the platform list, so a globally-disabled skill showed as
  enabled (unchecked) on any platform with a platform_disabled entry.
- tools/skills_tool._is_skill_disabled (gates whether skill_view loads a skill)
  ignored the global list when a platform list existed, so a globally-disabled
  skill could still be loaded on such a platform.

Both now union the global list with the platform list, matching
get_disabled_skill_names. An explicit empty platform list no longer re-enables
a globally-disabled skill — global disables hold on every platform (#46201).

Also: fix the now-stale get_disabled_skill_names docstring and drop a stray
blank line. Regression tests added for both sites (proven to fail on the old
replace semantics).

tools/skills_tool.py

@@ -583,11 +583,15 @@ def _is_skill_disabled(name: str, platform: str = None) -> bool:
         config = load_config()
         skills_cfg = config.get("skills", {})
         resolved_platform = platform or os.getenv("HERMES_PLATFORM") or _get_session_platform()
+        global_disabled = skills_cfg.get("disabled", [])
         if resolved_platform:
             platform_disabled = cfg_get(skills_cfg, "platform_disabled", resolved_platform)
             if platform_disabled is not None:
-                return name in platform_disabled
-        return name in skills_cfg.get("disabled", [])
+                # A globally-disabled skill stays disabled on every platform;
+                # the platform list adds to it rather than replacing it. Keep
+                # in sync with agent.skill_utils.get_disabled_skill_names.
+                return name in platform_disabled or name in global_disabled
+        return name in global_disabled
     except Exception:
         return False