language_models: Improve subscription states in the Agent configuration view (#30252)

This PR improves the subscription states in the Agent configuration view
to the new billing system.

Zed Free (legacy):

<img width="638" alt="Screenshot 2025-05-08 at 8 42 59 AM"
src="https://github.com/user-attachments/assets/7b62d4c1-2a9c-4c6a-aa8f-060730b6d7b3"
/>

Zed Free (new):

<img width="640" alt="Screenshot 2025-05-08 at 8 43 56 AM"
src="https://github.com/user-attachments/assets/8a48448e-813e-4633-955d-623d3e6d603c"
/>

Zed Pro trial:

<img width="641" alt="Screenshot 2025-05-08 at 8 45 52 AM"
src="https://github.com/user-attachments/assets/1ec7ee62-e954-48e7-8447-4584527307c9"
/>

Zed Pro:

<img width="636" alt="Screenshot 2025-05-08 at 8 47 21 AM"
src="https://github.com/user-attachments/assets/f934b2e3-0943-4b78-b8dc-0a31e731d8fb"
/>

Release Notes:

- agent: Improved the subscription-related information in the
configuration view.

crates/client/src/user.rs

@@ -11,7 +11,7 @@ use postage::{sink::Sink, watch};
 use rpc::proto::{RequestMessage, UsersResponse};
 use std::sync::{Arc, Weak};
 use text::ReplicaId;
-use util::TryFutureExt as _;
+use util::{TryFutureExt as _, maybe};
 
 pub type UserId = u64;
 
@@ -101,6 +101,7 @@ pub struct UserStore {
     participant_indices: HashMap<u64, ParticipantIndex>,
     update_contacts_tx: mpsc::UnboundedSender<UpdateContacts>,
     current_plan: Option<proto::Plan>,
+    subscription_period: Option<(DateTime<Utc>, DateTime<Utc>)>,
     trial_started_at: Option<DateTime<Utc>>,
     model_request_usage_amount: Option<u32>,
     model_request_usage_limit: Option<proto::UsageLimit>,
@@ -166,6 +167,7 @@ impl UserStore {
             by_github_login: Default::default(),
             current_user: current_user_rx,
             current_plan: None,
+            subscription_period: None,
             trial_started_at: None,
             model_request_usage_amount: None,
             model_request_usage_limit: None,
@@ -333,6 +335,13 @@ impl UserStore {
     ) -> Result<()> {
         this.update(&mut cx, |this, cx| {
             this.current_plan = Some(message.payload.plan());
+            this.subscription_period = maybe!({
+                let period = message.payload.subscription_period?;
+                let started_at = DateTime::from_timestamp(period.started_at as i64, 0)?;
+                let ended_at = DateTime::from_timestamp(period.ended_at as i64, 0)?;
+
+                Some((started_at, ended_at))
+            });
             this.trial_started_at = message
                 .payload
                 .trial_started_at
@@ -713,6 +722,10 @@ impl UserStore {
         self.current_plan
     }
 
+    pub fn subscription_period(&self) -> Option<(DateTime<Utc>, DateTime<Utc>)> {
+        self.subscription_period
+    }
+
     pub fn trial_started_at(&self) -> Option<DateTime<Utc>> {
         self.trial_started_at
     }