feat(display): verbose skill change notifications with content previews

When display.memory_notifications is set to 'verbose', skill_manage
notifications now show meaningful change details instead of just the
generic tool message.

Before (verbose mode):
  💾 📝 Patched SKILL.md in skill 'gogcli' (1 replacement).

After (verbose mode):
  💾 📝 Skill 'gogcli' patched: "old pitfall text..." → "new pitfall text..."

Changes:
- skill_manager_tool.py: _patch_skill() now includes old/new string
  previews (truncated to 200 chars) in the result via '_change' key.
  _create_skill() and _edit_skill() include skill description from
  frontmatter for verbose create/edit notifications.
- run_agent.py: Background review notification builder now reads the
  '_change' dict from skill tool results and formats descriptive
  notifications per action type (patch → old→new diff, create/edit →
  description preview). Falls back to generic message when _change
  data is unavailable (backwards compatible).

This is especially useful when subagents patch skills, since neither
the user nor the parent agent can see what the subagent changed.

tools/skill_manager_tool.py

@@ -598,11 +598,22 @@ def _create_skill(name: str, content: str, category: str = None) -> Dict[str, An
         shutil.rmtree(skill_dir, ignore_errors=True)
         return {"success": False, "error": scan_error}
 
+    # Extract description from frontmatter for verbose notifications
+    _desc = ""
+    try:
+        _fm_end = re.search(r'\n---\s*\n', content[3:])
+        if _fm_end:
+            _parsed = yaml.safe_load(content[3:_fm_end.start() + 3])
+            _desc = str(_parsed.get("description", ""))[:120]
+    except Exception:
+        pass
+
     result = {
         "success": True,
         "message": f"Skill '{name}' created.",
         "path": str(skill_dir.relative_to(SKILLS_DIR)),
         "skill_md": str(skill_md),
+        "_change": {"description": _desc},
     }
     if category:
         result["category"] = category
@@ -639,10 +650,21 @@ def _edit_skill(name: str, content: str) -> Dict[str, Any]:
             _atomic_write_text(skill_md, original_content)
         return {"success": False, "error": scan_error}
 
+    # Extract description from new content for verbose notifications
+    _desc = ""
+    try:
+        _fm_end = re.search(r'\n---\s*\n', content[3:])
+        if _fm_end:
+            _parsed = yaml.safe_load(content[3:_fm_end.start() + 3])
+            _desc = str(_parsed.get("description", ""))[:120]
+    except Exception:
+        pass
+
     return {
         "success": True,
-        "message": f"Skill '{name}' updated.",
+        "message": f"Skill '{name}' updated (full rewrite).",
         "path": str(existing["path"]),
+        "_change": {"description": _desc},
     }
 
 
@@ -734,10 +756,16 @@ def _patch_skill(
         _atomic_write_text(target, original_content)
         return {"success": False, "error": scan_error}
 
-    return {
+    result = {
         "success": True,
         "message": f"Patched {'SKILL.md' if not file_path else file_path} in skill '{name}' ({match_count} replacement{'s' if match_count > 1 else ''}).",
     }
+    # Include change previews for verbose notifications
+    result["_change"] = {
+        "old": old_string[:200] + ("…" if len(old_string) > 200 else ""),
+        "new": new_string[:200] + ("…" if len(new_string) > 200 else ""),
+    }
+    return result
 
 
 def _delete_skill(name: str, absorbed_into: Optional[str] = None) -> Dict[str, Any]: