fix(space-focus): 목표 안내를 상단 토스트로 통합

맥락:
- space 진입 직후 목표를 확정하면 하단 HUD 위에 GoalFlashOverlay가 노출되어 상단 토스트 흐름과 UI 기준점이 분리되어 있었다.

변경사항:
- GoalFlashOverlay 컴포넌트를 제거했다.
- SpaceFocusHudWidget에서 집중 진입 시점과 paused -> running 복귀 시점의 목표 안내를 onStatusMessage로 올리도록 변경했다.
- 목표 안내가 기존 FocusTopToast를 통해 상단에서 일관되게 보이도록 정리했다.

검증:
- npm run lint

세션-상태: 목표 안내가 하단 오버레이 없이 상단 토스트만 사용하는 상태
세션-다음: 실제 사운드/배경 적용 시 상단 상태 메시지 우선순위를 함께 점검
세션-리스크: 연속 상태 메시지가 짧은 간격으로 발생하면 토스트 큐 길이에 따라 일부 메시지가 뒤로 밀릴 수 있음

src/widgets/space-focus-hud/ui/GoalFlashOverlay.tsx

@@ -1,25 +0,0 @@
-import { cn } from '@/shared/lib/cn';
-
-interface GoalFlashOverlayProps {
-  goal: string;
-  visible: boolean;
-}
-
-export const GoalFlashOverlay = ({ goal, visible }: GoalFlashOverlayProps) => {
-  const normalizedGoal = goal.trim().length > 0 ? goal.trim() : '이번 한 조각을 잊지 마세요.';
-
-  return (
-    <div
-      className={cn(
-        'pointer-events-none fixed inset-x-0 z-20 flex justify-center px-4 transition-opacity duration-[240ms] ease-out motion-reduce:duration-0',
-        visible ? 'opacity-100' : 'opacity-0',
-      )}
-      style={{ bottom: 'calc(env(safe-area-inset-bottom, 0px) + 5.1rem)' }}
-      aria-hidden
-    >
-      <div className="rounded-full border border-white/12 bg-black/24 px-3 py-1.5 text-xs text-white/82 backdrop-blur-md">
-        이번 한 조각: <span className="text-white/92">{normalizedGoal}</span>
-      </div>
-    </div>
-  );
-};

src/widgets/space-focus-hud/ui/SpaceFocusHudWidget.tsx

@@ -1,9 +1,7 @@
-import { useCallback, useEffect, useRef, useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import type { HudStatusLinePayload } from '@/shared/lib/useHudStatusLine';
-import { useReducedMotion } from '@/shared/lib/useReducedMotion';
 import { SpaceTimerHudWidget } from '@/widgets/space-timer-hud';
 import { GoalCompleteSheet } from './GoalCompleteSheet';
-import { GoalFlashOverlay } from './GoalFlashOverlay';
 
 interface SpaceFocusHudWidgetProps {
   goal: string;
@@ -34,36 +32,14 @@ export const SpaceFocusHudWidget = ({
   onGoalUpdate,
   onStatusMessage,
 }: SpaceFocusHudWidgetProps) => {
-  const reducedMotion = useReducedMotion();
-  const [flashVisible, setFlashVisible] = useState(false);
   const [sheetOpen, setSheetOpen] = useState(false);
+  const visibleRef = useRef(false);
   const playbackStateRef = useRef<'running' | 'paused'>(playbackState);
-  const flashTimerRef = useRef<number | null>(null);
   const restReminderTimerRef = useRef<number | null>(null);
-
-  const triggerFlash = useCallback((durationMs: number) => {
-    if (reducedMotion || !visible) {
-      return;
-    }
-
-    setFlashVisible(true);
-
-    if (flashTimerRef.current) {
-      window.clearTimeout(flashTimerRef.current);
-    }
-
-    flashTimerRef.current = window.setTimeout(() => {
-      setFlashVisible(false);
-      flashTimerRef.current = null;
-    }, durationMs);
-  }, [reducedMotion, visible]);
+  const normalizedGoal = goal.trim().length > 0 ? goal.trim() : '집중을 시작해요.';
 
   useEffect(() => {
     return () => {
-      if (flashTimerRef.current) {
-        window.clearTimeout(flashTimerRef.current);
-        flashTimerRef.current = null;
-      }
       if (restReminderTimerRef.current) {
         window.clearTimeout(restReminderTimerRef.current);
         restReminderTimerRef.current = null;
@@ -72,56 +48,24 @@ export const SpaceFocusHudWidget = ({
   }, []);
 
   useEffect(() => {
-    if (!visible || reducedMotion) {
-      const rafId = window.requestAnimationFrame(() => {
-        setFlashVisible(false);
+    if (visible && !visibleRef.current) {
+      onStatusMessage({
+        message: `이번 한 조각 · ${normalizedGoal}`,
       });
-
-      return () => {
-        window.cancelAnimationFrame(rafId);
-      };
     }
 
-    const timeoutId = window.setTimeout(() => {
-      triggerFlash(2000);
-    }, 0);
-
-    return () => {
-      window.clearTimeout(timeoutId);
-    };
-  }, [visible, reducedMotion, triggerFlash]);
+    visibleRef.current = visible;
+  }, [normalizedGoal, onStatusMessage, visible]);
 
   useEffect(() => {
-    if (playbackStateRef.current === 'paused' && playbackState === 'running' && visible && !reducedMotion) {
-      const timeoutId = window.setTimeout(() => {
-        triggerFlash(1000);
-      }, 0);
-
-      playbackStateRef.current = playbackState;
-
-      return () => {
-        window.clearTimeout(timeoutId);
-      };
+    if (playbackStateRef.current === 'paused' && playbackState === 'running' && visible) {
+      onStatusMessage({
+        message: `이번 한 조각 · ${normalizedGoal}`,
+      });
     }
 
     playbackStateRef.current = playbackState;
-  }, [playbackState, reducedMotion, triggerFlash, visible]);
-
-  useEffect(() => {
-    const ENABLE_PERIODIC_FLASH = false;
-
-    if (!visible || reducedMotion || !ENABLE_PERIODIC_FLASH) {
-      return;
-    }
-
-    const intervalId = window.setInterval(() => {
-      triggerFlash(800);
-    }, 10 * 60 * 1000);
-
-    return () => {
-      window.clearInterval(intervalId);
-    };
-  }, [visible, reducedMotion, triggerFlash]);
+  }, [normalizedGoal, onStatusMessage, playbackState, visible]);
 
   if (!visible) {
     return null;
@@ -133,7 +77,6 @@ export const SpaceFocusHudWidget = ({
 
   return (
     <>
-      <GoalFlashOverlay goal={goal} visible={flashVisible} />
       <SpaceTimerHudWidget
         timerLabel={timerLabel}
         goal={goal}