feat: warp tunnel effect when entering portals (#250)

Adds three floating portal objects (Batcave, Workshop, The Void) around
the platform edge, each with an animated vortex interior shader. Clicking
a portal or pressing W triggers the fullscreen warp tunnel post-processing
effect — a swirling GLSL vortex with ring bands, 8-arm spiral, cyan/purple
color sweep, inward scene distortion, and a white flash at the peak.

- WarpTunnelShader + ShaderPass wired into existing EffectComposer
- Portal inner vortex: custom ShaderMaterial (5-arm spiral + ring bands)
- Raycaster click detection on portal disc meshes
- triggerWarp() state machine: build-up → hold → flash → fade-out
- 'W' key demo cycles through portals
- #warp-indicator HUD element with expanding letter-spacing pulse

Fixes #250

style.css

@@ -184,6 +184,36 @@ body.photo-mode #overview-indicator {
   100% { opacity: 0; transform: translate(-50%, -50%) scale(1); }
 }
 
+/* === WARP TUNNEL INDICATOR === */
+#warp-indicator {
+  display: none;
+  position: fixed;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+  color: #00aaff;
+  font-family: var(--font-body);
+  font-size: 13px;
+  letter-spacing: 0.35em;
+  text-transform: uppercase;
+  pointer-events: none;
+  z-index: 50;
+  padding: 6px 18px;
+  background: rgba(0, 0, 16, 0.65);
+  border: 1px solid #00aaff;
+  white-space: nowrap;
+}
+
+#warp-indicator.visible {
+  display: block;
+  animation: warp-pulse 0.4s ease-in-out infinite;
+}
+
+@keyframes warp-pulse {
+  0%, 100% { opacity: 0.8; letter-spacing: 0.35em; }
+  50%       { opacity: 1.0; letter-spacing: 0.5em; }
+}
+
 /* === CRT / CYBERPUNK OVERLAY === */
 .crt-overlay {
   position: fixed;