M2-T05: add SMTP test action API (POST /api/config/smtp/test)

- reuses send_smtp_test_email; tri-state result success(200)/config-error(400)/failed(502)
- session + CSRF protected; never echoes SMTP secrets
- SmtpTestResponse schema; regenerate openapi/
- extend tests/test_api_config.py (3 states + 401 + missing-CSRF 403)

openapi/openapi.yaml

@@ -222,6 +222,61 @@ paths:
             application/json:
               schema:
                 $ref: '#/components/schemas/HTTPValidationError'
+  /api/config/smtp/test:
+    post:
+      tags:
+      - api-config
+      summary: Post Smtp Test
+      description: 'Send a test SMTP email using the current runtime settings.
+
+
+        Returns a structured result indicating success or the category of failure.
+
+        Three possible outcomes:
+
+        - 200 { "result": "success", "message": ... }
+
+        - 400 { "result": "config-error", "message": ... }   (EmailConfigurationError)
+
+        - 502 { "result": "failed", "message": ... }          (EmailDeliveryError)
+
+
+        SMTP credentials are never echoed in the response.'
+      operationId: post_smtp_test_api_config_smtp_test_post
+      parameters:
+      - name: X-CSRF-Token
+        in: header
+        required: false
+        schema:
+          anyOf:
+          - type: string
+          - type: 'null'
+          title: X-Csrf-Token
+      responses:
+        '200':
+          description: Successful Response
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/SmtpTestResponse'
+        '400':
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/SmtpTestResponse'
+          description: Bad Request
+        '502':
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/SmtpTestResponse'
+          description: Bad Gateway
+        '422':
+          description: Validation Error
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/HTTPValidationError'
   /api/locations:
     get:
       tags:
@@ -1192,6 +1247,24 @@ components:
       - username
       - force_password_change
       title: SessionUser
+    SmtpTestResponse:
+      properties:
+        result:
+          type: string
+          enum:
+          - success
+          - config-error
+          - failed
+          title: Result
+        message:
+          type: string
+          title: Message
+      type: object
+      required:
+      - result
+      - message
+      title: SmtpTestResponse
+      description: Response from POST /api/config/smtp/test.
     StatusResponse:
       properties:
         status: