feat: make AI Copilot an optional dependency

This change makes AI Copilot features optional to reduce installation
size and support restricted environments.

Changes:
- Split AI dependencies into ai-requirements.txt
- Add ai-copilot optional dependency in pyproject.toml
- Add import protection in gns3server/agent/__init__.py
- Return 501 for AI endpoints when dependencies not installed
- Add gns3server-uninstall-ai-copilot command for cleanup
- Update README with installation and uninstallation instructions

Installation:
- Basic: pip install gns3-server
- With AI: pip install gns3-server[ai-copilot]
- Development: pip install gns3-server[ai-copilot,dev]

Uninstallation:
- gns3server-uninstall-ai-copilot

gns3server/agent/__init__.py

@@ -0,0 +1,75 @@
+#
+# 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 copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+Agent module with optional AI Copilot support.
+
+This module provides the AI Copilot functionality as an optional feature.
+If the AI dependencies are not installed, the module will be disabled but
+will not prevent the server from starting.
+
+Installation:
+    pip install gns3-server[ai-copilot]
+"""
+
+import logging
+
+# Feature flag: AI Copilot is available
+AI_COPILOT_AVAILABLE = False
+
+# Try to import AI Copilot components
+try:
+    from .gns3_copilot.project_agent_manager import get_project_agent_manager
+    from .gns3_copilot.project_agent_manager import ProjectAgentManager
+    AI_COPILOT_AVAILABLE = True
+except ImportError as e:
+    # AI dependencies not installed, disable AI Copilot feature
+    logging.warning(
+        f"AI Copilot dependencies not installed: {e}. "
+        "AI features will be disabled. Install with: pip install gns3-server[ai-copilot]"
+    )
+    AI_COPILOT_AVAILABLE = False
+
+    # Provide stub functions that raise helpful errors
+    async def get_project_agent_manager():
+        """
+        Get the global ProjectAgentManager singleton instance.
+
+        Raises:
+            RuntimeError: If AI Copilot dependencies are not installed
+        """
+        raise RuntimeError(
+            "AI Copilot is not available. "
+            "Install AI dependencies with: pip install gns3-server[ai-copilot]"
+        )
+
+    class ProjectAgentManager:
+        """
+        Stub class for ProjectAgentManager when AI dependencies are not installed.
+        """
+
+        def __init__(self):
+            raise RuntimeError(
+                "AI Copilot is not available. "
+                "Install AI dependencies with: pip install gns3-server[ai-copilot]"
+            )
+
+
+__all__ = [
+    "AI_COPILOT_AVAILABLE",
+    "get_project_agent_manager",
+    "ProjectAgentManager",
+]