feat(arr): add an env-only Podnapisi URL seam

ARR_PODNAPISI_URL, same shape as the existing tmdb_url seam: a test
harness can point the provider at a wiremock fake without touching
DESIGN.md §10's config surface.

crates/arr-daemon/src/main.rs

@@ -133,6 +133,7 @@ fn api_state(
             config.opensubtitles_api_key.clone(),
             config.opensubtitles_username.clone(),
             config.opensubtitles_password.clone(),
+            config.podnapisi_url.clone(),
         ))
         .with_translation_backends(translators.backends.clone())
         .with_jellyfin(jellyfin)
@@ -541,6 +542,7 @@ fn subtitle_action(
             config.opensubtitles_api_key.clone(),
             config.opensubtitles_username.clone(),
             config.opensubtitles_password.clone(),
+            config.podnapisi_url.clone(),
         ),
         translators.backends.clone(),
         arr_subs::Syncer::new().with_binary(config.alass_path.clone()),
@@ -564,10 +566,17 @@ fn subtitle_providers(
     opensubtitles_api_key: Option<String>,
     username: Option<String>,
     password: Option<String>,
+    podnapisi_url: Option<String>,
 ) -> Vec<std::sync::Arc<dyn arr_subs::Provider>> {
     let mut providers: Vec<std::sync::Arc<dyn arr_subs::Provider>> = Vec::new();
 
-    match arr_subs::Podnapisi::new() {
+    // `podnapisi_url` is the e2e-only seam (`ARR_PODNAPISI_URL`); absent, this
+    // is the real Podnapisi.net.
+    let mut builder = arr_subs::Podnapisi::builder();
+    if let Some(url) = podnapisi_url {
+        builder = builder.base_url(url);
+    }
+    match builder.build() {
         Ok(podnapisi) => providers.push(std::sync::Arc::new(podnapisi)),
         Err(error) => tracing::warn!(%error, "Podnapisi not available"),
     }