style: green theme for chat mascot, neutral back-to-top arrow

- Chat uses --accent-green (#27ae60) matching CV's green theme:
  header, user bubbles, send button, chip hover, input focus
- Dark theme uses deeper greens (#166b3a header, #1e8c4c interactions)
- Back-to-top arrow changed from green to neutral gray (#555555)
  to avoid visual conflict with the mascot button

static/css/04-interactive/_chat.css

@@ -34,7 +34,7 @@
     opacity: 1;
     transform: translateY(-3px);
     box-shadow: 0 6px 16px rgba(0, 0, 0, 0.4);
-    background: var(--accent-blue, #0066cc);
+    background: var(--accent-green, #27ae60);
 }
 
 /* Icon swap: show mascot by default, close when active */
@@ -44,7 +44,7 @@
 
 .chat-toggle-btn.mascot-active {
     opacity: 1;
-    background: var(--accent-blue, #0066cc);
+    background: var(--accent-green, #27ae60);
 }
 
 .chat-toggle-btn.mascot-active .chat-icon-open {
@@ -89,7 +89,7 @@
     align-items: center;
     gap: 8px;
     padding: 10px 14px;
-    background: var(--accent-blue, #0066cc);
+    background: var(--accent-green, #27ae60);
     color: #ffffff;
     font-family: 'Quicksand', sans-serif;
     font-size: 0.85rem;
@@ -167,7 +167,7 @@
 }
 
 .chat-user {
-    background: var(--accent-blue, #0066cc);
+    background: var(--accent-green, #27ae60);
     color: #fff;
     align-self: flex-end;
     border-bottom-right-radius: 2px;
@@ -243,9 +243,9 @@
 }
 
 .chat-chip:hover {
-    background: var(--accent-blue, #0066cc);
+    background: var(--accent-green, #27ae60);
     color: #fff;
-    border-color: var(--accent-blue, #0066cc);
+    border-color: var(--accent-green, #27ae60);
 }
 
 /* ==========================================================================
@@ -275,11 +275,11 @@
 }
 
 .chat-input:focus {
-    border-color: var(--accent-blue, #0066cc);
+    border-color: var(--accent-green, #27ae60);
 }
 
 .chat-send-btn {
-    background: var(--accent-blue, #0066cc);
+    background: var(--accent-green, #27ae60);
     color: #fff;
     border: none;
     border-radius: 50%;
@@ -295,7 +295,7 @@
 }
 
 .chat-send-btn:hover {
-    background: #004d99;
+    background: #1e8c4c;
 }
 
 /* ==========================================================================
@@ -332,7 +332,7 @@
 }
 
 .theme-clean .chat-header {
-    background: #003d7a;
+    background: #166b3a;
 }
 
 .theme-clean .chat-agent {
@@ -341,7 +341,7 @@
 }
 
 .theme-clean .chat-user {
-    background: #004d99;
+    background: #1e8c4c;
 }
 
 .theme-clean .chat-error {
@@ -372,9 +372,9 @@
 }
 
 .theme-clean .chat-chip:hover {
-    background: #004d99;
+    background: #1e8c4c;
     color: #fff;
-    border-color: #004d99;
+    border-color: #1e8c4c;
 }
 
 .theme-clean .chat-typing-dot {

static/css/04-interactive/_scroll-behavior.css

@@ -45,12 +45,12 @@
     opacity: 1;
     transform: translateY(-3px);
     box-shadow: 0 6px 16px rgba(0, 0, 0, 0.4);
-    background: #27ae60;
+    background: #555555;
 }
 
 .back-to-top.at-bottom {
     opacity: 1;
-    background: #27ae60;
+    background: #555555;
 }
 
 .back-to-top:active {