Look a group's title up once, not once per feed in it (#159)

subscriptions() names each feed derived from an OPML or a Patreon creator after its group when the
group has no folder, and asked feed_summary, three queries, for the group's title once for every
feed in it: the same title each time. Production's 32 Glass Cannon Network shows made that about 96
queries each time it ran, which is every feed list, every live update the page receives, every scan
and every wait between scans. It now asks once a group per call.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -1294,6 +1294,9 @@ pub async fn subscriptions(ctx: &Ctx) -> Result<Vec<Sub>> {
         .map(|(id, f)| Sub { id: id.clone(), cfg: f.clone(), managed: false })
         .collect();
 
+    // A group's title, once a group: asked for each feed in it, three queries a feed, it was about
+    // 96 for The Glass Cannon Network's 32 shows on every feed list, live update and scan (#159).
+    let mut group_titles = std::collections::HashMap::<String, String>::new();
     for m in ctx.db.managed_feeds().await? {
         if cfg.feeds.contains_key(&m.id) {
             continue; // promoted to config at some point; that entry wins
@@ -1307,7 +1310,13 @@ pub async fn subscriptions(ctx: &Ctx) -> Result<Vec<Sub>> {
         }
         let base = match parent.and_then(|p| p.folder.clone()) {
             Some(folder) => folder,
-            None => ctx.db.feed_summary(&m.group_id).await.ok().and_then(|s| s.title).unwrap_or_else(|| m.group_id.clone()),
+            None => {
+                if !group_titles.contains_key(&m.group_id) {
+                    let title = ctx.db.feed_summary(&m.group_id).await.ok().and_then(|s| s.title);
+                    group_titles.insert(m.group_id.clone(), title.unwrap_or_else(|| m.group_id.clone()));
+                }
+                group_titles[&m.group_id].clone()
+            }
         };
         let title = m.title.clone().unwrap_or_else(|| m.id.clone());
         out.push(Sub {