feat: add fault injection system and external skills repository

## Summary

Add a complete fault injection system for GNS3 Copilot, migrate all
skills from local Python files to an external Git repository with
hot reload support, and restructure Copilot API under /copilot/.

## Key Changes

### Fault Injection
- New troubleshooting_injection mode with InjectionSkillsTool
- 368 fault scenarios across 39 protocol categories
- Context-based filtering (LLM must pass topology protocols)

### External Skills Repository
- SkillsManager: Git clone/pull, version tracking, smart updates
- SkillsLoader: YAML skills + Markdown prompts from external repo
- Hot reload via POST /copilot/reload/skills
- Configurable via gns3_server.conf

### Architecture
- API unified under /copilot/ prefix
- SkillsManager moved from Controller to agent module
- Lazy initialization with startup background preload
- Per-command Git timeout, smart update checks
- Forbidden commands hot-reloadable from external repo
- 32 INFO logs downgraded to DEBUG

gns3server/api/routes/controller/copilot.py

@@ -0,0 +1,51 @@
+#
+# Copyright (C) 2025 GNS3 Technologies Inc.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+API routes for GNS3 Copilot global operations (non-project).
+"""
+
+import logging
+
+from fastapi import APIRouter, Depends
+from .dependencies.authentication import get_current_active_user
+
+log = logging.getLogger(__name__)
+
+router = APIRouter()
+
+
+@router.post(
+    "/reload/skills",
+    dependencies=[Depends(get_current_active_user)],
+)
+async def reload_skills() -> dict:
+    """
+    Hot reload skills and prompts from the external GNS3-Skills repository.
+
+    Reloads injection skills, system prompts, and forbidden commands
+    from the skills repository without restarting the server.
+    """
+    try:
+        from gns3server.agent.gns3_copilot.skills.registry import (
+            reload_skills_repository,
+        )
+
+        result = reload_skills_repository()
+    except ImportError:
+        return {"error": "AI Copilot is not available"}
+
+    return result