feat: 3D terminal emulator in Batcave alcove (#269)

Adds a WebGL Batcave terminal — a cave-like alcove with a console desk,
monitor frame, and canvas-texture terminal screen rendered in Three.js.

- Press [B] to fly camera to Batcave and focus the terminal
- Full keyboard capture with cursor blink and scanline CRT aesthetic
- Built-in commands: help, clear, status, agents, whoami, uptime, date,
  ls, ping, exit/quit
- Terminal input is isolated from scene key-bindings (Tab/P/sovereignty)
  while focused
- Green phosphor glow light pulses from the screen into the cave

Fixes #269

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

style.css

@@ -184,6 +184,43 @@ body.photo-mode #overview-indicator {
   100% { opacity: 0; transform: translate(-50%, -50%) scale(1); }
 }
 
+/* === BATCAVE TERMINAL INDICATOR === */
+#batcave-indicator {
+  display: none;
+  position: fixed;
+  bottom: 16px;
+  left: 50%;
+  transform: translateX(-50%);
+  color: #00ff44;
+  font-family: var(--font-body);
+  font-size: 11px;
+  letter-spacing: 0.2em;
+  text-transform: uppercase;
+  pointer-events: none;
+  z-index: 20;
+  border: 1px solid #00ff44;
+  padding: 4px 12px;
+  background: rgba(0, 13, 4, 0.8);
+  white-space: nowrap;
+  animation: batcave-pulse 1.5s ease-in-out infinite;
+}
+
+#batcave-indicator.visible {
+  display: block;
+}
+
+.batcave-hint {
+  margin-left: 12px;
+  color: #005522;
+  font-size: 10px;
+  letter-spacing: 0.1em;
+}
+
+@keyframes batcave-pulse {
+  0%, 100% { opacity: 0.75; box-shadow: 0 0 6px rgba(0,255,68,0.3); }
+  50% { opacity: 1; box-shadow: 0 0 12px rgba(0,255,68,0.6); }
+}
+
 /* === CRT / CYBERPUNK OVERLAY === */
 .crt-overlay {
   position: fixed;