feat: add notification for task status (#19965)

## Description

Send a notification to the workspace owner when an AI task’s app state
becomes `Working` or `Idle`.
An AI task is identified by a workspace build with `HasAITask = true`
and `AITaskSidebarAppID` matching the agent app’s ID.

## Changes

* Add `TemplateTaskWorking` notification template.
* Add `TemplateTaskIdle` notification template.
* Add `GetLatestWorkspaceAppStatusesByAppID` SQL query to get the
workspace app statuses ordered by latest first.
* Update `PATCH /workspaceagents/me/app-status` to enqueue:
  * `TemplateTaskWorking` when state transitions to `working`
  * `TemplateTaskIdle` when state transitions to `idle`
* Notification labels include:
  * `task`: task initial prompt
  * `workspace`: workspace name
* Notification dedupe: include a minute-bucketed timestamp (UTC
truncated to the minute) in the enqueue data to allow identical content
to resend within the same day (but not more than once per minute).

Closes: https://github.com/coder/coder/issues/19776

coderd/notifications/testdata/rendered-templates/webhook/TemplateTaskIdle.json.golden

@@ -0,0 +1,33 @@
+{
+  "_version": "1.1",
+  "msg_id": "00000000-0000-0000-0000-000000000000",
+  "payload": {
+    "_version": "1.2",
+    "notification_name": "Task Idle",
+    "notification_template_id": "00000000-0000-0000-0000-000000000000",
+    "user_id": "00000000-0000-0000-0000-000000000000",
+    "user_email": "bobby@coder.com",
+    "user_name": "Bobby",
+    "user_username": "bobby",
+    "actions": [
+      {
+        "label": "View task",
+        "url": "http://test.com/tasks/bobby/my-workspace"
+      },
+      {
+        "label": "View workspace",
+        "url": "http://test.com/@bobby/my-workspace"
+      }
+    ],
+    "labels": {
+      "task": "my-task",
+      "workspace": "my-workspace"
+    },
+    "data": {},
+    "targets": null
+  },
+  "title": "Task 'my-workspace' is idle",
+  "title_markdown": "Task 'my-workspace' is idle",
+  "body": "The task 'my-task' is idle and ready for input.",
+  "body_markdown": "The task 'my-task' is idle and ready for input."
+}

coderd/notifications/testdata/rendered-templates/webhook/TemplateTaskWorking.json.golden

@@ -0,0 +1,33 @@
+{
+  "_version": "1.1",
+  "msg_id": "00000000-0000-0000-0000-000000000000",
+  "payload": {
+    "_version": "1.2",
+    "notification_name": "Task Working",
+    "notification_template_id": "00000000-0000-0000-0000-000000000000",
+    "user_id": "00000000-0000-0000-0000-000000000000",
+    "user_email": "bobby@coder.com",
+    "user_name": "Bobby",
+    "user_username": "bobby",
+    "actions": [
+      {
+        "label": "View task",
+        "url": "http://test.com/tasks/bobby/my-workspace"
+      },
+      {
+        "label": "View workspace",
+        "url": "http://test.com/@bobby/my-workspace"
+      }
+    ],
+    "labels": {
+      "task": "my-task",
+      "workspace": "my-workspace"
+    },
+    "data": {},
+    "targets": null
+  },
+  "title": "Task 'my-workspace' is working",
+  "title_markdown": "Task 'my-workspace' is working",
+  "body": "The task 'my-task' transitioned to a working state.",
+  "body_markdown": "The task 'my-task' transitioned to a working state."
+}