Add example agent tool preview (#28984)

This PR adds an example of rendering previews for tools using the new
Agent ToolCard style.

![CleanShot 2025-04-17 at 13 03
12@2x](https://github.com/user-attachments/assets/d4c7d266-cc32-4038-9170-f3e070fce60e)

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <git@maxdeviant.com>

typos.toml

@@ -19,6 +19,9 @@ extend-exclude = [
     # Some crate names are flagged as typos.
     "crates/indexed_docs/src/providers/rustdoc/popular_crates.txt",
 
+    # Some mock data is flagged as typos.
+    "crates/assistant_tools/src/web_search_tool.rs",
+
     # Stripe IDs are flagged as typos.
     "crates/collab/src/db/tests/processed_stripe_event_tests.rs",
     # Not our typos.