FRE-4762: Update API endpoints to match ProtonMail v4 contract

- Change all paths from /api/messages to /mail/v4/messages
- Update HTTP methods: GET for reads, PUT for updates, DELETE for deletes
- Fix response structures to match official API format
- Add X-HTTP-Method-Override header for list operations

Changes align with go-proton-api reference implementation.

internal/mail/client.go

@@ -56,12 +56,13 @@ func (c *Client) ListMessages(req ListMessagesRequest) (*ListMessagesResponse, e
 		return nil, fmt.Errorf("failed to marshal request: %w", err)
 	}
 
-	reqURL := fmt.Sprintf("%s/api/messages", c.baseURL)
+	reqURL := fmt.Sprintf("%s/mail/v4/messages", c.baseURL)
 	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return nil, fmt.Errorf("failed to create request: %w", err)
 	}
 	httpReq.Header.Set("Content-Type", "application/json")
+	httpReq.Header.Set("X-HTTP-Method-Override", "GET")
 
 	resp, err := c.apiClient.Do(httpReq)
 	if err != nil {
@@ -83,21 +84,15 @@ func (c *Client) ListMessages(req ListMessagesRequest) (*ListMessagesResponse, e
 }
 
 func (c *Client) GetMessage(messageID string, passphrase string) (*Message, error) {
-	body := map[string]string{
-		"Passphrase": passphrase,
+	var result struct {
+		Message Message `json:"Message"`
 	}
 
-	jsonBody, err := json.Marshal(body)
-	if err != nil {
-		return nil, fmt.Errorf("failed to marshal request: %w", err)
-	}
-
-	reqURL := fmt.Sprintf("%s/api/messages/%s", c.baseURL, url.QueryEscape(messageID))
-	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
+	reqURL := fmt.Sprintf("%s/mail/v4/messages/%s", c.baseURL, url.QueryEscape(messageID))
+	httpReq, err := http.NewRequest("GET", reqURL, nil)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create request: %w", err)
 	}
-	httpReq.Header.Set("Content-Type", "application/json")
 
 	resp, err := c.apiClient.Do(httpReq)
 	if err != nil {
@@ -110,14 +105,11 @@ func (c *Client) GetMessage(messageID string, passphrase string) (*Message, erro
 		return nil, fmt.Errorf("failed to read response: %w", err)
 	}
 
-	var result struct {
-		Data Message `json:"Data"`
-	}
 	if err := json.Unmarshal(respBody, &result); err != nil {
 		return nil, fmt.Errorf("failed to parse response: %w", err)
 	}
 
-	return &result.Data, nil
+	return &result.Message, nil
 }
 
 func (c *Client) Send(req SendRequest) error {
@@ -154,7 +146,7 @@ func (c *Client) Send(req SendRequest) error {
 		return fmt.Errorf("failed to marshal request: %w", err)
 	}
 
-	reqURL := fmt.Sprintf("%s/api/messages", c.baseURL)
+	reqURL := fmt.Sprintf("%s/mail/v4/messages", c.baseURL)
 	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return fmt.Errorf("failed to create request: %w", err)
@@ -176,14 +168,21 @@ func (c *Client) Send(req SendRequest) error {
 }
 
 func (c *Client) MoveToTrash(messageID string, passphrase string) error {
-	formData := url.Values{}
-	formData.Set("Passphrase", passphrase)
-	reqURL := fmt.Sprintf("%s/api/messages/%s/movetotrash", c.baseURL, url.QueryEscape(messageID))
-	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBufferString(formData.Encode()))
+	body := map[string]string{
+		"Passphrase": passphrase,
+	}
+
+	jsonBody, err := json.Marshal(body)
+	if err != nil {
+		return fmt.Errorf("failed to marshal request: %w", err)
+	}
+
+	reqURL := fmt.Sprintf("%s/mail/v4/messages/%s/trash", c.baseURL, url.QueryEscape(messageID))
+	httpReq, err := http.NewRequest("PUT", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return fmt.Errorf("failed to create request: %w", err)
 	}
-	httpReq.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	httpReq.Header.Set("Content-Type", "application/json")
 
 	resp, err := c.apiClient.Do(httpReq)
 	if err != nil {
@@ -200,8 +199,8 @@ func (c *Client) MoveToTrash(messageID string, passphrase string) error {
 }
 
 func (c *Client) PermanentlyDelete(messageID string) error {
-	reqURL := fmt.Sprintf("%s/api/messages/%s/delete", c.baseURL, url.QueryEscape(messageID))
-	httpReq, err := http.NewRequest("POST", reqURL, nil)
+	reqURL := fmt.Sprintf("%s/mail/v4/messages/%s", c.baseURL, url.QueryEscape(messageID))
+	httpReq, err := http.NewRequest("DELETE", reqURL, nil)
 	if err != nil {
 		return fmt.Errorf("failed to create request: %w", err)
 	}
@@ -242,7 +241,7 @@ func (c *Client) SaveDraft(draft Draft, passphrase string) (string, error) {
 		return "", fmt.Errorf("failed to marshal request: %w", err)
 	}
 
-	reqURL := fmt.Sprintf("%s/api/messages", c.baseURL)
+	reqURL := fmt.Sprintf("%s/mail/v4/messages", c.baseURL)
 	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return "", fmt.Errorf("failed to create request: %w", err)
@@ -261,27 +260,29 @@ func (c *Client) SaveDraft(draft Draft, passphrase string) (string, error) {
 	}
 
 	var result struct {
-		Data struct {
+		Message struct {
 			MessageID string `json:"MessageID"`
-		} `json:"Data"`
+		} `json:"Message"`
 	}
 	if err := json.Unmarshal(respBody, &result); err != nil {
 		return "", fmt.Errorf("failed to parse response: %w", err)
 	}
 
-	return result.Data.MessageID, nil
+	return result.Message.MessageID, nil
 }
 
 func (c *Client) UpdateDraft(messageID string, draft Draft, passphrase string) error {
 	body := map[string]interface{}{
-		"Passphrase": passphrase,
-		"Subject":    draft.Subject,
-		"To":         draft.To,
-		"Body":       draft.Body,
+		"Message": map[string]interface{}{
+			"Passphrase": passphrase,
+			"Subject":    draft.Subject,
+			"To":         draft.To,
+			"Body":       draft.Body,
+		},
 	}
 
 	if len(draft.CC) > 0 {
-		body["CC"] = draft.CC
+		body["Message"].(map[string]interface{})["CC"] = draft.CC
 	}
 
 	jsonBody, err := json.Marshal(body)
@@ -289,8 +290,8 @@ func (c *Client) UpdateDraft(messageID string, draft Draft, passphrase string) e
 		return fmt.Errorf("failed to marshal request: %w", err)
 	}
 
-	reqURL := fmt.Sprintf("%s/api/messages/%s", c.baseURL, url.QueryEscape(messageID))
-	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
+	reqURL := fmt.Sprintf("%s/mail/v4/messages/%s", c.baseURL, url.QueryEscape(messageID))
+	httpReq, err := http.NewRequest("PUT", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return fmt.Errorf("failed to create request: %w", err)
 	}
@@ -311,14 +312,21 @@ func (c *Client) UpdateDraft(messageID string, draft Draft, passphrase string) e
 }
 
 func (c *Client) SendDraft(messageID string, passphrase string) error {
-	formData := url.Values{}
-	formData.Set("Passphrase", passphrase)
-	reqURL := fmt.Sprintf("%s/api/messages/%s/send", c.baseURL, url.QueryEscape(messageID))
-	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBufferString(formData.Encode()))
+	body := map[string]string{
+		"Passphrase": passphrase,
+	}
+
+	jsonBody, err := json.Marshal(body)
+	if err != nil {
+		return fmt.Errorf("failed to marshal request: %w", err)
+	}
+
+	reqURL := fmt.Sprintf("%s/mail/v4/messages/%s", c.baseURL, url.QueryEscape(messageID))
+	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return fmt.Errorf("failed to create request: %w", err)
 	}
-	httpReq.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	httpReq.Header.Set("Content-Type", "application/json")
 
 	resp, err := c.apiClient.Do(httpReq)
 	if err != nil {
@@ -357,7 +365,7 @@ func (c *Client) SearchMessages(req SearchRequest) (*SearchResponse, error) {
 		return nil, fmt.Errorf("failed to marshal request: %w", err)
 	}
 
-	reqURL := fmt.Sprintf("%s/api/messages/search", c.baseURL)
+	reqURL := fmt.Sprintf("%s/mail/v4/messages/search", c.baseURL)
 	httpReq, err := http.NewRequest("POST", reqURL, bytes.NewBuffer(jsonBody))
 	if err != nil {
 		return nil, fmt.Errorf("failed to create request: %w", err)