feat(03-03): add SVG forest background and 4x3 grid HTML/CSS structure

- SVG woodland background with sky gradient, clouds, sun, trees, hills, ground
- 4x3 CSS grid overlay for forest element placement
- Fade-in + scale-up animation keyframes for new elements

index.html

@@ -34,6 +34,30 @@
 					<img id="forest-greeting-avatar" class="companion-area__avatar" src="" alt="">
 					<p id="forest-greeting-text" class="companion-area__text"></p>
 				</div>
+				<div class="forest__scene" id="forest-scene">
+					<svg class="forest__bg" viewBox="0 0 800 400" xmlns="http://www.w3.org/2000/svg">
+						<defs>
+							<linearGradient id="sky-grad" x1="0" y1="0" x2="0" y2="1">
+								<stop offset="0%" stop-color="#E8F4FD"/>
+								<stop offset="100%" stop-color="#F0F8E8"/>
+							</linearGradient>
+						</defs>
+						<rect x="0" y="0" width="800" height="300" fill="url(#sky-grad)"/>
+						<ellipse cx="150" cy="60" rx="60" ry="25" fill="white" opacity="0.5"/>
+						<ellipse cx="550" cy="80" rx="70" ry="20" fill="white" opacity="0.4"/>
+						<circle cx="700" cy="50" r="30" fill="#F8E8A0" opacity="0.6"/>
+						<g opacity="0.3">
+							<ellipse cx="80" cy="240" rx="40" ry="60" fill="#7DB87D"/>
+							<ellipse cx="720" cy="250" rx="35" ry="55" fill="#6DA86D"/>
+							<ellipse cx="400" cy="230" rx="45" ry="70" fill="#8DC88D"/>
+						</g>
+						<ellipse cx="200" cy="320" rx="250" ry="80" fill="#A8D8A8"/>
+						<ellipse cx="650" cy="330" rx="200" ry="60" fill="#B8E0B0"/>
+						<rect x="0" y="300" width="800" height="100" fill="#C8E6C0" rx="0"/>
+					</svg>
+					<div class="forest__grid" id="forest-grid">
+					</div>
+				</div>
 				<div class="forest__level-map" id="level-map">
 					<!-- Level cards rendered dynamically -->
 				</div>

src/styles/main.css

@@ -378,6 +378,69 @@ h3 {
 	line-height: 1.4;
 }
 
+/* Forest Scene */
+.forest__scene {
+	position: relative;
+	width: 100%;
+	max-width: 800px;
+	margin: 0 auto 1.5rem;
+	border-radius: 16px;
+	overflow: hidden;
+	box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
+}
+
+.forest__bg {
+	display: block;
+	width: 100%;
+	height: auto;
+}
+
+.forest__grid {
+	position: absolute;
+	top: 0;
+	left: 0;
+	width: 100%;
+	height: 100%;
+	display: grid;
+	grid-template-columns: repeat(4, 1fr);
+	grid-template-rows: repeat(3, 1fr);
+	padding: 1rem;
+	gap: 0.5rem;
+}
+
+.forest__element {
+	display: flex;
+	align-items: center;
+	justify-content: center;
+}
+
+.forest__element img {
+	max-width: 100%;
+	max-height: 100%;
+	object-fit: contain;
+	border-radius: 8px;
+	filter: drop-shadow(0 2px 4px rgba(0, 0, 0, 0.15));
+}
+
+.forest__element--new {
+	animation: forest-element-appear 1.2s ease-out forwards;
+}
+
+@keyframes forest-element-appear {
+	0% {
+		opacity: 0;
+		transform: scale(0.3);
+	}
+	60% {
+		opacity: 1;
+		transform: scale(1.05);
+	}
+	100% {
+		opacity: 1;
+		transform: scale(1);
+	}
+}
+
 /* Keyboard */
 .keyboard {
 	display: flex;