refactor(site): drop RenderData's url field, source_url already carries it

Every adapter built RenderData { url } from the exact value it then moved into Fetched.source_url — a copy of the same canonical URL held in two places, feeding one placeholder. caption_with reads {url} from self.source_url now and the field is gone from the struct (bsky's and twitter's halves of this change landed with their caption commits; their render builders no longer set it either).

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

@@ -289,7 +289,6 @@ impl From<model::Item> for Fetched {
             sensitive: false,
             site_id: "bilibili",
             render_data: Some(RenderData {
-                url,
                 author: encode_text(&author).into_owned(),
                 author_url,
                 title: encode_text(&title).into_owned(),

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

@@ -133,7 +133,6 @@ impl From<model::Note> for Fetched {
             sensitive,
             site_id: "misskey",
             render_data: Some(RenderData {
-                url,
                 author: encode_text(&author).into_owned(),
                 author_url: author_url.clone(),
                 title: String::new(),

crates/x-media/src/site/mod.rs

@@ -69,13 +69,14 @@ pub struct Fetched {
 ///
 /// `author`, `title`, `content` and `tags` come from the site API (post
 /// text, display names, descriptions) and are HTML-escaped at construction.
-/// `url` and `author_url` stay raw: they are canonical URLs the adapter
-/// builds from numeric ids and API-constrained handles/DIDs, so they carry
-/// no escapable character — the bot's `/test` report relies on that when it
-/// embeds them.
+/// `author_url` stays raw: it is a canonical URL the adapter builds from
+/// numeric ids and API-constrained handles/DIDs, so it carries no escapable
+/// character — the bot's `/test` report relies on that when it embeds it.
+/// `{url}` needs no copy here: [`Fetched::source_url`] is the same canonical
+/// URL every adapter would have handed this struct, and `caption_with` reads
+/// it from there.
 #[derive(Debug)]
 pub(crate) struct RenderData {
-    pub url: String,
     pub author: String,
     pub author_url: String,
     pub title: String,
@@ -125,7 +126,7 @@ impl Fetched {
             (Some(data), false) => caption_from_fields(
                 format,
                 "",
-                &data.url,
+                &self.source_url,
                 &data.author,
                 &data.author_url,
                 &data.title,

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

@@ -289,7 +289,6 @@ impl From<Illustration> for Fetched {
             .collect::<Vec<_>>()
             .join(" ");
         let render_data = Some(crate::site::RenderData {
-            url: url.clone(),
             author: encode_text(&illustration.author).into_owned(),
             author_url: author_url.clone(),
             title: encode_text(&illustration.title).into_owned(),