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.sql.go

@@ -18841,6 +18841,45 @@ func (q *sqlQuerier) UpsertWorkspaceAppAuditSession(ctx context.Context, arg Ups
 	return new_or_stale, err
 }
 
+const getLatestWorkspaceAppStatusesByAppID = `-- name: GetLatestWorkspaceAppStatusesByAppID :many
+SELECT id, created_at, agent_id, app_id, workspace_id, state, message, uri
+FROM workspace_app_statuses
+WHERE app_id = $1::uuid
+ORDER BY created_at DESC, id DESC
+`
+
+func (q *sqlQuerier) GetLatestWorkspaceAppStatusesByAppID(ctx context.Context, appID uuid.UUID) ([]WorkspaceAppStatus, error) {
+	rows, err := q.db.QueryContext(ctx, getLatestWorkspaceAppStatusesByAppID, appID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []WorkspaceAppStatus
+	for rows.Next() {
+		var i WorkspaceAppStatus
+		if err := rows.Scan(
+			&i.ID,
+			&i.CreatedAt,
+			&i.AgentID,
+			&i.AppID,
+			&i.WorkspaceID,
+			&i.State,
+			&i.Message,
+			&i.Uri,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Close(); err != nil {
+		return nil, err
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const getLatestWorkspaceAppStatusesByWorkspaceIDs = `-- name: GetLatestWorkspaceAppStatusesByWorkspaceIDs :many
 SELECT DISTINCT ON (workspace_id)
   id, created_at, agent_id, app_id, workspace_id, state, message, uri