Fix severities endpoint to use V1 API

The severities endpoints (list and get) are part of incident.io's V1 API,
not V2. This fix temporarily switches the base URL to V1 when making
severities requests.

Changes:
- Update ListSeverities() to use V1 API endpoint
- Update GetSeverity() to use V1 API endpoint
- Add comments explaining the API version difference

This resolves the 404 errors when calling list_severities tool.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: 2 people

internal/incidentio/severities.go

@@ -14,6 +14,12 @@ type ListSeveritiesResponse struct {
 
 // ListSeverities returns all severities
 func (c *Client) ListSeverities() (*ListSeveritiesResponse, error) {
+	// Note: Severities are under V1 API, not V2
+	// We need to temporarily change the base URL for this request
+	originalBaseURL := c.BaseURL()
+	c.SetBaseURL("https://api.incident.io/v1")
+	defer func() { c.SetBaseURL(originalBaseURL) }()
+	
 	respBody, err := c.doRequest("GET", "/severities", nil, nil)
 	if err != nil {
 		return nil, err
@@ -29,6 +35,12 @@ func (c *Client) ListSeverities() (*ListSeveritiesResponse, error) {
 
 // GetSeverity retrieves a specific severity by ID
 func (c *Client) GetSeverity(id string) (*Severity, error) {
+	// Note: Severities are under V1 API, not V2
+	// We need to temporarily change the base URL for this request
+	originalBaseURL := c.BaseURL()
+	c.SetBaseURL("https://api.incident.io/v1")
+	defer func() { c.SetBaseURL(originalBaseURL) }()
+	
 	respBody, err := c.doRequest("GET", fmt.Sprintf("/severities/%s", id), nil, nil)
 	if err != nil {
 		return nil, err