Rename assistant2 to agent (#27887)

This PR renames the `assistant2` crate to `agent`.

Release Notes:

- N/A

Cargo.toml

@@ -2,11 +2,11 @@
 resolver = "2"
 members = [
     "crates/activity_indicator",
+    "crates/agent",
     "crates/anthropic",
     "crates/askpass",
     "crates/assets",
     "crates/assistant",
-    "crates/assistant2",
     "crates/assistant_context_editor",
     "crates/assistant_eval",
     "crates/assistant_settings",
@@ -207,12 +207,12 @@ edition = "2024"
 #
 
 activity_indicator = { path = "crates/activity_indicator" }
+agent = { path = "crates/agent" }
 ai = { path = "crates/ai" }
 anthropic = { path = "crates/anthropic" }
 askpass = { path = "crates/askpass" }
 assets = { path = "crates/assets" }
 assistant = { path = "crates/assistant" }
-assistant2 = { path = "crates/assistant2" }
 assistant_context_editor = { path = "crates/assistant_context_editor" }
 assistant_eval = { path = "crates/assistant_eval" }
 assistant_settings = { path = "crates/assistant_settings" }