feat: add packet filter management tool for GNS3-Copilot fault injection

Add comprehensive packet filter management functionality to GNS3-Copilot,
enabling AI-powered fault injection scenarios with network simulation
capabilities like latency, packet loss, and corruption.

## Changes

### New Features
- **GNS3PacketFilterTool**: New LangChain tool for managing packet filters
  on GNS3 links with support for delay, packet loss, corruption,
  frequency_drop, and BPF filtering
  - Actions: get_available, set, get, clear
  - Integrated into troubleshooting_injection mode for fault scenarios

### API Integration
- **Link.available_filters()**: Added method to custom_gns3fy.py Link class
  - Queries available filter types for specific links
  - API v3+ only (raises ValueError for v2 connectors)
  - Returns filter definitions with parameters and constraints

### Tool Integration
- Added GNS3PacketFilterTool to TROUBLESHOOTING_INJECTION_MODE_TOOLS
- Positioned as 3rd tool in fault injection workflow
- Optimized for troubleshooting practice scenarios

## Files Modified
- gns3server/agent/gns3_copilot/agent/gns3_copilot.py
- gns3server/agent/gns3_copilot/gns3_client/custom_gns3fy.py
- gns3server/agent/gns3_copilot/tools_v2/__init__.py

## Files Added
- gns3server/agent/gns3_copilot/tools_v2/gns3_packet_filter.py

## Testing
- All validation tests passed
- Version checking verified (v3+ only)
- Tool integration confirmed in troubleshooting mode

gns3server/agent/gns3_copilot/gns3_client/custom_gns3fy.py

@@ -1042,6 +1042,66 @@ class Link:
         # Update object
         self._update(_response.json())
 
+    @verify_connector_and_id
+    def available_filters(self) -> list[dict[str, Any]]:
+        """
+        Gets the list of available packet filters for this link.
+
+        **NOTE:** This endpoint is only available in GNS3 API v3 or later.
+        Attempting to call this method with a v2 connector will raise an error.
+
+        **Required Attributes:**
+
+        - `project_id`
+        - `connector` (must be API v3 or later)
+        - `link_id`
+
+        **Returns:**
+
+        List of available filter types with their parameters (e.g., frequency_drop,
+        packet_loss, delay, corrupt, bpf).
+
+        **Example:**
+
+        ```python
+        >>> link = Link(project_id=<pr_id>, link_id=<link_id>, connector=<connector>)
+        >>> filters = link.available_filters()
+        >>> print(filters)
+        [
+            {
+                "type": "frequency_drop",
+                "name": "Frequency drop",
+                "description": "It will drop everything with a -1 frequency...",
+                "parameters": [...]
+            },
+            ...
+        ]
+        ```
+        """
+        _conn = self.connector
+        _project_id = self.project_id
+
+        if _conn is None:
+            raise ValueError("Gns3Connector not assigned under 'connector'")
+        if _project_id is None:
+            raise ValueError("Need to submit project_id")
+
+        # Check API version - available_filters endpoint is only available in v3+
+        if not hasattr(_conn, "api_version") or _conn.api_version < 3:
+            raise ValueError(
+                "The available_filters() method requires GNS3 API v3 or later. "
+                f"Current connector version: v{getattr(_conn, 'api_version', 2)}. "
+                "Please use api_version=3 when creating the Gns3Connector."
+            )
+
+        _url = (
+            f"{_conn.base_url}/projects/{_project_id}/links/{self.link_id}/"
+            "available_filters"
+        )
+        _response = _conn.http_call("get", _url)
+
+        return cast(list[dict[str, Any]], _response.json())
+
 
 @dataclass(config=config)
 class Node: