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).

hermes_cli/skills_config.py

@@ -25,7 +25,13 @@ PLATFORMS = {k: info.label for k, info in _PLATFORMS.items() if k != "api_server
 # ─── Config Helpers ───────────────────────────────────────────────────────────
 
 def get_disabled_skills(config: dict, platform: Optional[str] = None) -> Set[str]:
-    """Return disabled skill names. Platform-specific list falls back to global."""
+    """Return disabled skill names: the global list unioned with the
+    platform-specific list when a platform is given.
+
+    A globally-disabled skill stays disabled on every platform, so the
+    platform list adds to the global list rather than replacing it. This
+    mirrors ``agent.skill_utils.get_disabled_skill_names``.
+    """
     skills_cfg = config.get("skills", {})
     global_disabled = set(skills_cfg.get("disabled", []))
     if platform is None:
@@ -33,7 +39,7 @@ def get_disabled_skills(config: dict, platform: Optional[str] = None) -> Set[str
     platform_disabled = cfg_get(skills_cfg, "platform_disabled", platform)
     if platform_disabled is None:
         return global_disabled
-    return set(platform_disabled)
+    return global_disabled | set(platform_disabled)
 
 
 def save_disabled_skills(config: dict, disabled: Set[str], platform: Optional[str] = None):