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/config.rs

@@ -24,6 +24,31 @@ pub struct Config {
     pub sandbox: SandboxConfig,
     pub search: SearchConfig,
     pub lsp: LspConfig,
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    pub hooks: Vec<HookConfig>,
+}
+
+/// A shell command run on an agent event (see hooks.rs).
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct HookConfig {
+    /// pre_tool, post_tool, user_prompt or stop.
+    pub event: String,
+    /// Tool name pattern for tool events ("*", "bash", "edit|write", "mcp__*").
+    #[serde(default = "star")]
+    pub matcher: String,
+    pub command: String,
+    #[serde(default = "sixty")]
+    pub timeout_secs: u64,
+    #[serde(default = "yes")]
+    pub enabled: bool,
+}
+
+fn star() -> String {
+    "*".into()
+}
+
+fn sixty() -> u64 {
+    60
 }
 
 /// Language servers for diagnostics after edits.