Upload images through the API, and from the MCP server

POST /api/v1/media stores an image where the panel keeps a page's and
answers with the path to send as `featured_image`. Without it the MCP
server could create a page but never give it a picture. The file goes
through Media::for(), so it is processed, served and pruned like one
uploaded in the panel.

Two ways in, one per request: a multipart `file`, or JSON with a `url`
the API downloads itself. JPEG, PNG, WebP, GIF or AVIF only, decided
from the bytes; no SVG, which is a document that can carry script.

The URL is fetched from inside the stack's network, so RemoteImage
guards it: HTTPS only, every resolved address must be public, the
connection is pinned to the checked address with CURLOPT_RESOLVE so a
changing DNS answer cannot swap in a private one, redirects are not
followed, and the body is read to a ceiling whatever its headers say.

Uploading needs permission to write pages. MediaPolicy::create stays
false, so the panel gains no free-standing "new file" button.

In the MCP server a multipart binary field becomes `<field>_path` over
stdio: the server reads the file from the caller's disk and sends it
as multipart, instead of the model pushing base64 through its context.
Over HTTP the server's disk is not the caller's, so only `body.url` is
offered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lang/es/rules.php

@@ -28,4 +28,17 @@ return [
     'pages' => [
         'cannot_publish' => 'No tienes permiso para publicar páginas.',
     ],
+
+    'media' => [
+        'not_an_image' => 'El fichero no es una imagen JPEG, PNG, WebP, GIF o AVIF.',
+        'remote' => [
+            'https_only' => 'La URL de la imagen tiene que empezar por https://.',
+            'unresolvable' => 'No se ha podido resolver el dominio de la URL.',
+            'private' => 'La URL apunta a una dirección privada o reservada: solo se descargan imágenes de direcciones públicas.',
+            'unreachable' => 'No se ha podido conectar con la URL.',
+            'redirect' => 'La URL redirige a otra dirección. Usa la dirección final de la imagen.',
+            'status' => 'La URL ha respondido :status en lugar de la imagen.',
+            'too_large' => 'La imagen supera el máximo de :max KB.',
+        ],
+    ],
 ];