fix(posimai-dev): aurora visibility, scrollbar styling

- Force xterm-viewport/screen/canvas to transparent so container aurora shows through
- theme.background: 'transparent' (was rgba with 0 alpha — some renderers ignored it)
- Scrollbar: 5px, violet 40% opacity, thin Firefox fallback via scrollbar-color

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

posimai-dev/index.html

@@ -111,10 +111,17 @@
         #terminal-container .xterm { height: 100%; }
         #terminal-container .xterm-viewport { border-radius: 8px 8px 0 0; }
 
-        .xterm-viewport::-webkit-scrollbar { width: 4px; }
+        /* xterm 内部の不透明レイヤーを透明化 → aurora が透ける */
-        .xterm-viewport::-webkit-scrollbar-track { background: transparent; }
+        #terminal-container .xterm-viewport,
-        .xterm-viewport::-webkit-scrollbar-thumb { background: rgba(167,139,250,0.25); border-radius: 2px; }
+        #terminal-container .xterm-screen,
-        .xterm-viewport::-webkit-scrollbar-thumb:hover { background: rgba(167,139,250,0.5); }
+        #terminal-container .xterm-screen canvas { background: transparent !important; }
+
+        /* スクロールバー — 右端に固定、細く鮮明に */
+        .xterm-viewport { scrollbar-width: thin; scrollbar-color: rgba(167,139,250,0.35) transparent; }
+        .xterm-viewport::-webkit-scrollbar { width: 5px; }
+        .xterm-viewport::-webkit-scrollbar-track { background: rgba(255,255,255,0.03); border-radius: 3px; }
+        .xterm-viewport::-webkit-scrollbar-thumb { background: rgba(167,139,250,0.4); border-radius: 3px; }
+        .xterm-viewport::-webkit-scrollbar-thumb:hover { background: rgba(167,139,250,0.7); }
 
         /* ── Input wrapper (relative anchor for slash popup) ── */
         .input-wrapper {
@@ -427,7 +434,7 @@
         cursorBlink: true,
         allowTransparency: true,
         theme: {
-            background: 'rgba(12, 18, 33, 0.0)',
+            background: 'transparent',
             foreground: '#F3F4F6',
             cursor: '#A78BFA',
             selectionBackground: 'rgba(167,139,250,0.3)',