fix: update Discord webhook integration to use non-optional IDs and improve embed generation

crates/jetstream/src/repo.rs

···
                     state,
                     &WebhookEnvelope {
                         r#type: "scrobble.created".to_string(),
-                        id: Some(commit.rkey.clone()),
+                        id: commit.rkey.clone(),
                         data: ScrobbleData {
                             user: discord::model::User {
                                 did: did.to_string(),

crates/jetstream/src/webhook/discord/mod.rs

···
 use crate::webhook::discord::model::*;
 use reqwest::Client;
 
-pub fn embed_from_scrobble(s: &ScrobbleData) -> DiscordEmbed {
-    let url = s
-        .track
-        .spotify_url
-        .as_ref()
-        .or(s.track.tidal_url.as_ref())
-        .or(s.track.youtube_url.as_ref())
-        .cloned();
+pub fn embed_from_scrobble(s: &ScrobbleData, rkey: &str) -> DiscordEmbed {
+    let url = format!("https://rocksky.app/{}/scrobble/{}", s.user.did, rkey);
 
     let mut desc = format!("**{}**\nby {}", esc(&s.track.title), esc(&s.track.artist));
     desc.push_str(&format!("\non *{}*", esc(&s.track.album)));

crates/jetstream/src/webhook/discord/model.rs

···
 pub struct WebhookEnvelope {
     #[serde(default)]
     pub r#type: String,
-    #[serde(default)]
-    pub id: Option<String>,
+    pub id: String,
     #[serde(default)]
     pub delivered_at: Option<String>,
     pub data: ScrobbleData,
···
 #[derive(Debug, Serialize)]
 pub struct DiscordEmbed {
     pub title: String,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub url: Option<String>,
+    pub url: String,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub description: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]

crates/jetstream/src/webhook_worker.rs

···
             match brpop_once(st.clone(), 1).await {
                 Ok(Some(json_str)) => {
                     if let Ok(env) = serde_json::from_str::<WebhookEnvelope>(&json_str) {
-                        embeds.push(discord::embed_from_scrobble(&env.data));
+                        embeds.push(discord::embed_from_scrobble(&env.data, &env.id));
                     }
                 }
                 Ok(None) => break,