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/store.rs

@@ -1,6 +1,6 @@
 //! SQLite persistence for sessions and messages.
 
-use crate::types::{Message, Session, now_ms};
+use crate::types::{Message, Part, Session, now_ms};
 use serde::Serialize;
 use serde_json::{Value, json};
 use anyhow::Result;
@@ -178,6 +178,57 @@ impl Store {
         Ok(out)
     }
 
+    /// Full-text search over titles and message texts of the sessions a user
+    /// can see (None = all). Returns (session, snippet) pairs, newest first.
+    pub fn search_sessions(&self, user: Option<&str>, q: &str) -> Result<Vec<(Session, String)>> {
+        let needle = q.to_lowercase();
+        let like = format!("%{}%", q.replace('\\', "\\\\").replace('%', "\\%").replace('_', "\\_"));
+        let conn = self.conn.lock().unwrap();
+        let mut stmt = conn.prepare(
+            "SELECT s.data,
+                    (SELECT m.data FROM messages m WHERE m.session_id = s.id AND m.data LIKE ?2 ESCAPE '\\' ORDER BY m.seq DESC LIMIT 1)
+             FROM sessions s
+             WHERE s.parent_id IS NULL
+               AND (?1 IS NULL OR s.owner_id = ?1 OR s.id IN (SELECT session_id FROM session_shares WHERE user_id = ?1))
+               AND (s.data LIKE ?2 ESCAPE '\\' OR EXISTS (SELECT 1 FROM messages m WHERE m.session_id = s.id AND m.data LIKE ?2 ESCAPE '\\'))
+             ORDER BY s.updated_at DESC LIMIT 50",
+        )?;
+        let rows = stmt.query_map(rusqlite::params![user, like], |r| Ok((r.get::<_, String>(0)?, r.get::<_, Option<String>>(1)?)))?;
+        let mut out = Vec::new();
+        for row in rows {
+            let (sdata, mdata) = row?;
+            let session: Session = serde_json::from_str(&sdata)?;
+            // Snippet from the visible text of the matching message (not JSON keys).
+            let mut snippet = String::new();
+            if let Some(m) = mdata.and_then(|d| serde_json::from_str::<Message>(&d).ok()) {
+                for p in &m.parts {
+                    let text = match p {
+                        Part::Text { text } | Part::Summary { text } | Part::Reasoning { text, .. } => text.as_str(),
+                        Part::ToolResult { content, .. } => content.as_str(),
+                        _ => continue,
+                    };
+                    if let Some(i) = text.to_lowercase().find(&needle) {
+                        let mut a = i.saturating_sub(60);
+                        while !text.is_char_boundary(a) {
+                            a -= 1;
+                        }
+                        let mut b = (i + needle.len() + 100).min(text.len());
+                        while !text.is_char_boundary(b) {
+                            b += 1;
+                        }
+                        snippet = format!("{}{}{}", if a > 0 { "…" } else { "" }, text[a..b].replace('\n', " "), if b < text.len() { "…" } else { "" });
+                        break;
+                    }
+                }
+            }
+            if snippet.is_empty() && !session.title.to_lowercase().contains(&needle) {
+                continue; // matched only JSON structure (keys, ids)
+            }
+            out.push((session, snippet));
+        }
+        Ok(out)
+    }
+
     pub fn delete_session(&self, id: &str) -> Result<()> {
         let conn = self.conn.lock().unwrap();
         // Child sessions (subagents) go with their parent.