feat(fsd): 허브·스페이스 중심 UI 목업 구조로 재편

맥락:

- 기존 라우트/컴포넌트 구조를 FSD 기준으로 정리하고, /app 허브와 /space 집중 화면 중심의 목업 흐름을 구성하기 위해

변경사항:

- App Router 구조를 /landing, /app, /space, /stats, /settings 중심으로 재배치

- entities/session/room/user 더미 데이터와 타입 정의 추가

- features(커스텀 입장, 룸 선택, 체크인, 리액션, 30초 리스타트 등) 단위로 로직 분리

- widgets(허브, 룸 갤러리, 타이머 HUD, 툴 도크 등) 조합형 UI 추가

- shared 공용 UI(Button/Chip/Modal/Toast 등) 및 유틸(cn/useReducedMotion) 정비

- 로그인 후 이동 경로를 /dashboard 에서 /app 으로 변경

- README를 현재 프로젝트 구조/라우트/구현 범위 기준으로 갱신

검증:

- npx tsc --noEmit

세션-상태: 허브·스페이스 목업이 FSD 레이어로 동작 가능하도록 정리됨

세션-다음: /space 상단 및 도크의 인원 수 카피를 분위기형 카피로 후속 정리

세션-리스크: build는 네트워크 환경에서 Google Fonts fetch 실패 가능

src/widgets/space-shell/ui/SpaceSkeletonWidget.tsx

@@ -0,0 +1,106 @@
+'use client';
+
+import { useEffect, useMemo, useState } from 'react';
+import Link from 'next/link';
+import { useSearchParams } from 'next/navigation';
+import { getRoomBackgroundStyle, getRoomById, ROOM_THEMES } from '@/entities/room';
+import { SOUND_PRESETS } from '@/entities/session';
+import { cn } from '@/shared/lib/cn';
+import { SpaceTimerHudWidget } from '@/widgets/space-timer-hud';
+import { SpaceToolsDockWidget } from '@/widgets/space-tools-dock';
+
+export const SpaceSkeletonWidget = () => {
+  const searchParams = useSearchParams();
+
+  const roomId = searchParams.get('room') ?? ROOM_THEMES[0].id;
+  const goal = searchParams.get('goal') ?? '오늘은 한 조각만 집중해요';
+  const timerLabel = searchParams.get('timer') ?? '25/5';
+  const soundFromQuery = searchParams.get('sound');
+
+  const room = useMemo(() => getRoomById(roomId) ?? ROOM_THEMES[0], [roomId]);
+
+  const defaultSoundId =
+    SOUND_PRESETS.find((preset) => preset.id === soundFromQuery)?.id ??
+    SOUND_PRESETS[0].id;
+
+  const [selectedSoundId, setSelectedSoundId] = useState(defaultSoundId);
+
+  useEffect(() => {
+    setSelectedSoundId(defaultSoundId);
+  }, [defaultSoundId]);
+
+  return (
+    <div className="relative min-h-screen overflow-x-hidden overflow-y-hidden text-white">
+      <div
+        aria-hidden
+        className="absolute inset-0 w-full"
+        style={getRoomBackgroundStyle(room)}
+      />
+      <div aria-hidden className="absolute inset-0 w-full bg-slate-950/62" />
+      <div
+        aria-hidden
+        className="absolute inset-0 w-full opacity-35"
+        style={{
+          backgroundImage:
+            "url('/textures/grain.png'), repeating-linear-gradient(0deg, rgba(255,255,255,0.045) 0 1px, transparent 1px 2px)",
+        }}
+      />
+
+      <div className="relative z-10 flex min-h-screen flex-col pr-14">
+        <header className="flex items-center justify-between border-b border-white/12 bg-slate-950/35 px-4 py-3 backdrop-blur-lg sm:px-6">
+          <div className="flex items-center gap-2">
+            <span className="inline-flex h-8 w-8 items-center justify-center rounded-full border border-white/30 bg-white/10 text-xs font-semibold">
+              V
+            </span>
+            <p className="text-sm font-semibold tracking-tight">VibeRoom</p>
+          </div>
+
+          <Link
+            href="/app"
+            className="rounded-lg border border-white/30 px-3 py-1.5 text-xs text-white/85 transition hover:bg-white/10"
+          >
+            허브로 돌아가기
+          </Link>
+        </header>
+
+        <main className="flex-1 px-4 pt-6 sm:px-6">
+          <div className="mx-auto w-full max-w-5xl">
+            <div className="space-y-1">
+              <p className="text-xs uppercase tracking-[0.14em] text-white/65">Current Room</p>
+              <p className="text-lg font-semibold text-white">{room.name}</p>
+              <p className="text-xs text-white/70">현재 {room.activeMembers}명 함께 집중 중</p>
+            </div>
+          </div>
+        </main>
+
+        <footer className="border-t border-white/12 bg-slate-950/42 px-4 py-3 backdrop-blur-md sm:px-6">
+          <div className="mx-auto flex w-full max-w-5xl flex-wrap gap-2">
+            {SOUND_PRESETS.map((preset) => (
+              <button
+                key={preset.id}
+                type="button"
+                onClick={() => setSelectedSoundId(preset.id)}
+                className={cn(
+                  'rounded-full border px-3 py-1.5 text-xs transition-colors',
+                  selectedSoundId === preset.id
+                    ? 'border-sky-200/75 bg-sky-300/25 text-sky-50'
+                    : 'border-white/24 bg-white/8 text-white/82 hover:bg-white/14',
+                )}
+              >
+                {preset.label}
+              </button>
+            ))}
+          </div>
+        </footer>
+      </div>
+
+      <SpaceTimerHudWidget timerLabel={timerLabel} goal={goal} />
+
+      <SpaceToolsDockWidget
+        roomName={room.name}
+        activeMembers={room.activeMembers}
+        presence={room.presence}
+      />
+    </div>
+  );
+};