thread view: Add UI refinements (#35754)

More notably around how we render tool calls. Nothing too drastic,
though.

Release Notes:

- N/A

crates/icons/src/icons.rs

@@ -261,7 +261,6 @@ pub enum IconName {
     TodoComplete,
     TodoPending,
     TodoProgress,
-    ToolBulb,
     ToolCopy,
     ToolDeleteFile,
     ToolDiagnostics,
@@ -273,6 +272,7 @@ pub enum IconName {
     ToolRegex,
     ToolSearch,
     ToolTerminal,
+    ToolThink,
     ToolWeb,
     Trash,
     Triangle,