agent: Improve action confirmation UX (#27932)

This PR makes the command permission prompt part of the tool card and
allow users to straight away change the `always_allow_tool_actions`
setting via the "Always Allow" button from that card. If that button is
clicked, that setting is turned on, and any command that requires
permission from that point on will auto-run.

Additionally, if a bash command spans multiple lines, we show the line
count at the end of the command string. (Note: this is not perfect yet
because it can likely be not visible by default, but we didn't think
this was a major blocker for now. We'll work on improving this next).

### Thread View

<img
src="https://github.com/user-attachments/assets/00f93c39-990f-4b79-84ec-0427b997167f"
width="500"/>

### Settings View

<img
src="https://github.com/user-attachments/assets/52d32435-7c8d-4ab4-a319-6cabc007267b"
width="500"/>


Release Notes:

- N/A

---------

Co-authored-by: Thomas Mickley-Doyle <tmickleydoyle@gmail.com>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Antonio Scandurra <me@as-cii.com>

crates/assistant_settings/src/assistant_settings.rs

@@ -325,6 +325,15 @@ impl AssistantSettingsContent {
         }
     }
 
+    pub fn set_always_allow_tool_actions(&mut self, allow: bool) {
+        let AssistantSettingsContent::Versioned(VersionedAssistantSettingsContent::V2(settings)) =
+            self
+        else {
+            return;
+        };
+        settings.always_allow_tool_actions = Some(allow);
+    }
+
     pub fn set_profile(&mut self, profile_id: AgentProfileId) {
         let AssistantSettingsContent::Versioned(VersionedAssistantSettingsContent::V2(settings)) =
             self