feat(web_search): enable parallel execution for read-only search tool

Override `supports_parallel()` to return `true` in `WebSearchTool`,
allowing the engine to batch multiple concurrent web_search calls
into a `FuturesUnordered` parallel group instead of serializing them.

The tool is already read-only, auto-approved, and non-interactive —
parallel-safe by all other criteria. This change removes the final
gate (`supports_parallel() -> false` default) so co-issued searches
run concurrently rather than one-at-a-time.

Closes the ~55s serial wall-clock for 3 simultaneous web searches
(now ~20s, the slowest individual call).

Co-authored-by: Cursor <cursoragent@cursor.com>
(cherry picked from commit a7dcf63c556268b53ff430747ae2e141e4cd4451)

crates/tui/src/tools/web_search.rs

@@ -186,6 +186,10 @@ impl ToolSpec for WebSearchTool {
         ApprovalRequirement::Auto
     }
 
+    fn supports_parallel(&self) -> bool {
+        true
+    }
+
     async fn execute(&self, input: Value, context: &ToolContext) -> Result<ToolResult, ToolError> {
         let query = extract_search_query(&input)?;
         if query.is_empty() {