test: share the photo payload fixture, drop two test-only aliases

The one-photo MediaItemPayload literal was written out at six sites across
the urls and send test modules; ctx::test_support::photo_item holds it once.
permanent_error now delegates to api_error (it stays a fn pointer because
that is what MockSender::scripted takes), misskey's x_media_site_id wrapper
is gone in favour of the function it renamed, and PixivAPI is no longer
re-exported -- nothing outside pixiv/api.rs names it.

crates/xmedia-bot/src/ctx.rs

@@ -50,6 +50,7 @@ pub static CONTEXT: LazyLock<AppContext<'static>> =
 pub(crate) mod test_support {
     use super::*;
     use crate::link_cache::{CachedMedia, CachedMediaKind, CachedPost};
+    use crate::send::MediaItemPayload;
     use crate::state::EditMessage;
     use std::sync::Arc;
     use teloxide::{ApiError, RequestError};
@@ -64,6 +65,18 @@ pub(crate) mod test_support {
         RequestError::Api(ApiError::Unknown(message.to_string()))
     }
 
+    /// One photo payload item: `media` in the two flags the tests vary (no
+    /// smaller variant, since that is the field most tests leave alone —
+    /// `send`'s own tests build that case directly).
+    pub(crate) fn photo_item(media: &str, has_spoiler: bool, file_id: bool) -> MediaItemPayload {
+        MediaItemPayload::Photo {
+            media: media.to_string(),
+            has_spoiler,
+            fallback_url: None,
+            file_id,
+        }
+    }
+
     /// The cached post every test that touches the link cache starts from: one
     /// photo with a Telegram file id at the canonical URL (key `twitter:1`).
     /// Tests that need another field mutate the returned value.