revert(web): drop run build phase hints, keep the dots loader

The preparing / loading_tools / starting text hints (PR #304) read as
noise; those phases fall back to the bouncing-dots loader again.
Backend keeps emitting the status SSE events — sandbox_creating /
sandbox_failed still render, and the events stay available for future
UI. i18n keys removed with the last consumer.

Author: xfgong

frontend/packages/web/components/chat/AssistantMessage.tsx

@@ -739,15 +739,7 @@ export function AssistantMessage({
             )}
             {isStreaming && (
               <div data-testid="loading-indicator" className="flex items-center gap-1 pl-1 h-6">
-                {statusPhase === 'preparing' || statusPhase === 'loading_tools' ? (
-                  <span className="text-xs text-muted-foreground animate-pulse">
-                    {statusPhase === 'preparing' ? t('runPreparing') : t('runLoadingTools')}
-                  </span>
-                ) : statusPhase === 'starting' ? (
-                  <span className="text-xs text-muted-foreground animate-pulse">
-                    {t('runStarting')}
-                  </span>
-                ) : statusPhase === 'sandbox_creating' ? (
+                {statusPhase === 'sandbox_creating' ? (
                   <span className="text-xs text-muted-foreground animate-pulse">
                     {t('sandboxPreparing')}
                   </span>

frontend/packages/web/messages/en.json

@@ -346,10 +346,7 @@
       "openPage": "Open memory",
       "openPageAria": "Go to memory page",
       "empty": "No memories yet"
-    },
-    "runPreparing": "Preparing...",
-    "runLoadingTools": "Loading tools...",
-    "runStarting": "Contacting model..."
+    }
   },
   "subagent": {
     "cluster": "Agent cluster",

frontend/packages/web/messages/zh.json

@@ -346,10 +346,7 @@
       "openPage": "打开记忆页",
       "openPageAria": "跳转到记忆页面",
       "empty": "暂无记忆"
-    },
-    "runPreparing": "正在准备...",
-    "runLoadingTools": "正在加载工具...",
-    "runStarting": "正在请求模型..."
+    }
   },
   "subagent": {
     "cluster": "Agent 集群",