Add hooks, @file mentions, session search/fork/export, follow-scroll

- Hooks ([[hooks]]): pre_tool, post_tool, user_prompt, stop; sandboxed, exit 2 blocks
- @file mentions with autocomplete; mentioned files/folders are attached to the prompt
- Session full-text search in the sidebar, fork into a copy, export as Markdown/JSON
- Chat follows the newest message until the user scrolls up; jump-to-latest button
- SVG activity spark and thinking icon instead of Unicode/emoji glyphs
- File search ranks name matches first and returns relative paths

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

server/src/files.rs

@@ -399,20 +399,32 @@ pub async fn search(Extension(user): Extension<User>, State(app): State<AppState
         return Ok(Json(json!([])));
     }
     let hits = tokio::task::spawn_blocking(move || {
-        let mut out = Vec::new();
+        // Matches on the name or the relative path; name prefix matches first.
+        let mut found: Vec<(u8, usize, Value)> = Vec::new();
         for e in ignore::WalkBuilder::new(&root).hidden(true).build().flatten() {
             if e.depth() == 0 {
                 continue;
             }
             let name = e.file_name().to_string_lossy().to_lowercase();
-            if name.contains(&needle) {
-                out.push(json!({"path": e.path(), "is_dir": e.file_type().is_some_and(|t| t.is_dir())}));
-                if out.len() >= 200 {
-                    break;
-                }
+            let rel = e.path().strip_prefix(&root).unwrap_or(e.path()).to_string_lossy().to_string();
+            let rel_l = rel.to_lowercase();
+            let rank = if name.starts_with(&needle) {
+                0
+            } else if name.contains(&needle) {
+                1
+            } else if rel_l.contains(&needle) {
+                2
+            } else {
+                continue;
+            };
+            let is_dir = e.file_type().is_some_and(|t| t.is_dir());
+            found.push((rank, rel.len(), json!({"path": e.path(), "rel": rel, "is_dir": is_dir})));
+            if found.len() >= 2000 {
+                break;
             }
         }
-        out
+        found.sort_by_key(|(r, l, _)| (*r, *l));
+        found.into_iter().take(200).map(|(_, _, v)| v).collect::<Vec<_>>()
     })
     .await?;
     Ok(Json(json!(hits)))