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/database/queries/workspaceapps.sql

@@ -73,6 +73,12 @@ RETURNING *;
 -- name: GetWorkspaceAppStatusesByAppIDs :many
 SELECT * FROM workspace_app_statuses WHERE app_id = ANY(@ids :: uuid [ ]);
 
+-- name: GetLatestWorkspaceAppStatusesByAppID :many
+SELECT *
+FROM workspace_app_statuses
+WHERE app_id = @app_id::uuid
+ORDER BY created_at DESC, id DESC;
+
 -- name: GetLatestWorkspaceAppStatusesByWorkspaceIDs :many
 SELECT DISTINCT ON (workspace_id)
   *