fix: sticky continue button at bottom of forest screen

- Continue button uses position: sticky bottom: 1rem so it stays visible
- Mute button moved higher (bottom: 70px) to avoid overlap
- Forest content remains scrollable

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/styles/main.css

@@ -251,6 +251,8 @@ h3 {
 }
 
 .forest__continue-btn {
+	position: sticky;
+	bottom: 1rem;
 	padding: 1rem 3rem;
 	border-radius: 12px;
 	background: var(--accent-green);
@@ -261,6 +263,8 @@ h3 {
 	font-size: 1.3rem;
 	cursor: pointer;
 	transition: transform 0.2s ease;
+	box-shadow: 0 -4px 12px rgba(0, 0, 0, 0.1);
+	z-index: 10;
 }
 
 .forest__continue-btn:hover {
@@ -979,7 +983,7 @@ h3 {
 /* Mute button — fixed position, always accessible */
 .mute-btn {
 	position: fixed;
-	bottom: 16px;
+	bottom: 70px;
 	right: 16px;
 	z-index: 100;
 	width: 44px;