feat: integrate Resend for OTP email delivery and update configuration

docs/API_SPEC.md

@@ -32,7 +32,7 @@ Authorization: Bearer <token>
 - `POST /auth/register`
   citizen registration without password
 - `POST /auth/otp/request`
-  sends OTP through Mailpit
+  queues OTP email through configured mail provider
 - `POST /auth/otp/verify`
   consumes OTP, returns bearer token
 - `POST /auth/cie/start`

docs/ARCHITECTURE.md

@@ -24,7 +24,7 @@ generate public read-only intervention links.
 
 ## Runtime Model
 - Auth uses bearer tokens from `api_tokens`.
-- OTP login uses `otp_challenges` and Mailpit in local dev.
+- OTP login uses `otp_challenges` and async email delivery through configured mail provider.
 - CIE login uses external Django RP service:
   - Visione creates local `state`
   - Django RP completes CIE/OIDC and sends signed identity payload to Visione

docs/LLM_CONTEXT.md

@@ -30,7 +30,7 @@ public revocable link generated by operator/admin.
 ## Current Auth Model
 - Registration creates `citizen`.
 - Login path:
-  - OTP email via Mailpit
+  - OTP email via configured mail provider
   - CIE via external `spid-cie-oidc-django` relying party service
 - Auth token: bearer token from `api_tokens`
 - Banned users cannot authenticate.

docs/openapi/visione.openapi.yaml

@@ -2582,7 +2582,7 @@
     },
     "/api/v1/auth/otp/request": {
       "post": {
-        "description": "Sends a one-time code by email through Mailpit locally.",
+        "description": "Queues a one-time code by email through configured mail provider.",
         "operationId": "AuthController.requestOtp",
         "parameters": [ ],
         "requestBody": {