refactor(x-media): share the HTTP-status error mapping

twitter, twitter auth and bsky carried the same 404/410 -> NotFound,
401/403 -> Blocked, else Transient block (comments included).
site::status_error holds it once. bilibili and misskey keep their own
matches: neither maps 404/410 and each has a status the others do not
(412 risk control, 400 + NO_SUCH_NOTE), so routing them through the shared
block would have reclassified those statuses for the user.

crates/x-media/src/site/bsky/interface.rs

@@ -321,13 +321,7 @@ pub async fn fetch(handle: &str, rkey: &str) -> Result<Post, FetchError> {
     // 404/410 = gone (permanent); 429/5xx = transient and retried by fetch.
     let status = response.status();
     if !status.is_success() {
-        return match status.as_u16() {
-            404 | 410 => Err(FetchError::NotFound),
-            // A refusal or an auth demand is not a bad moment: retrying it
-            // three times only delays an error the user has to see.
-            401 | 403 => Err(FetchError::Blocked),
-            _ => Err(FetchError::Transient(format!("bsky status {status}"))),
-        };
+        return Err(crate::site::status_error("bsky", status));
     }
     let text = response.text().await?;
     Post::from_json(&text, rkey.to_string())