fix(chat): reveal the home page once after a two-phase bootstrap

The loading screen now owns every wait: starter questions, today's
starlanguage and the rectification entry summary are fetched in a prepare
phase before reveal (4s budget, static fallbacks), the rectification chunk is
warmed, recent sessions are prefetched, and no component spinner remains
after the page appears. BUG-479.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0193vBv6w5MV2cifdTUu9H5P

frontend/src/components/starter-home.tsx

@@ -22,7 +22,6 @@ export type StarterHomeProps = {
   readonly dailyStarlanguageQuestion: string;
   readonly dailyStarlanguageTrend: string;
   readonly dailyStarlanguageAction: string;
-  readonly dailyStarlanguageBusy: boolean;
   readonly productEntrypointsDisabled: boolean;
   readonly startDailyStarlanguageConsultation: () => void;
   readonly rectificationCardLabel: string;
@@ -47,7 +46,6 @@ export function StarterHome({
   dailyStarlanguageQuestion,
   dailyStarlanguageTrend,
   dailyStarlanguageAction,
-  dailyStarlanguageBusy,
   productEntrypointsDisabled,
   startDailyStarlanguageConsultation,
   rectificationCardLabel,
@@ -85,7 +83,6 @@ export function StarterHome({
                       <div className="product-entrypoint-copy">
                         <h2 id="daily-starlanguage-title">{natalMinuteAvailable ? "今日星语" : "每日运势"}</h2>
                         <p
-                          aria-busy={dailyStarlanguageBusy}
                           role={natalMinuteAvailable && dailyStarlanguage.kind !== "ready" ? "status" : undefined}
                         >{natalMinuteAvailable ? dailyStarlanguageTrend : "看看今天的整体节奏、适合推进的事和需要留意的地方。"}</p>
                       </div>