fix(ui): tone down InteractPrompt and support empty label

- Smaller boxes (36x36 key + 36px-tall label) instead of the previous
  oversized white pills.
- Dark translucent background (rgba(10, 12, 20, 0.55)) with a 1px
  white outline (rgba(255, 255, 255, 0.7)), no border-radius and
  white text so the prompt blends with the dark UI instead of being a
  bright blob over the 3D scene.
- Key cube now has a 3D keyboard-key effect (inset top highlight +
  inset bottom darkening + small bottom drop) so it reads as a
  physical key.
- Key and label are visually separated (gap: 8px) but share the same
  height for alignment.
- InteractPrompt no longer renders the label box when focused.label is
  empty/whitespace, so callers can show the key prompt alone.

src/components/ui/InteractPrompt.tsx

@@ -9,10 +9,14 @@ export function InteractPrompt(): React.JSX.Element | null {
   if (cameraMode !== "player") return null;
   if (!focused || holding || focused.kind !== "trigger") return null;
 
+  const label = focused.label?.trim() ?? "";
+
   return (
     <div className="interact-prompt" aria-live="polite">
       <kbd className="interact-prompt__key">{INTERACT_KEY.toUpperCase()}</kbd>
-      <span className="interact-prompt__label">{focused.label}</span>
+      {label.length > 0 ? (
+        <span className="interact-prompt__label">{label}</span>
+      ) : null}
     </div>
   );
 }

src/index.css

@@ -813,41 +813,43 @@ canvas {
   left: 50%;
   transform: translateX(-50%);
   display: flex;
-  align-items: center;
-  gap: 12px;
+  align-items: stretch;
+  gap: 8px;
   pointer-events: none;
   z-index: 10;
 }
 
-.interact-prompt__key {
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  width: 64px;
-  height: 64px;
-  background: rgba(255, 255, 255, 0.92);
-  border-radius: 12px;
-  box-shadow: 0 6px 24px rgba(0, 0, 0, 0.25);
-  font-family: "Inter", sans-serif;
-  font-size: 32px;
-  font-weight: 900;
-  font-style: normal;
-  color: #0a0a0a;
-  letter-spacing: 0;
-}
-
+.interact-prompt__key,
 .interact-prompt__label {
   display: inline-flex;
   align-items: center;
-  padding: 16px 24px;
-  background: rgba(255, 255, 255, 0.92);
-  border-radius: 12px;
-  box-shadow: 0 6px 24px rgba(0, 0, 0, 0.25);
+  justify-content: center;
+  height: 36px;
+  background: rgba(10, 12, 20, 0.55);
+  border: 1px solid rgba(255, 255, 255, 0.7);
   font-family: "Inter", sans-serif;
-  font-size: 22px;
+  color: #ffffff;
+}
+
+.interact-prompt__key {
+  width: 36px;
+  font-size: 15px;
   font-weight: 900;
-  color: #0a0a0a;
+  font-style: normal;
   letter-spacing: 0;
+  /* 3D keyboard key effect: top highlight, bottom inner darkening,
+     and a thin bottom drop so the key reads as physically pressed-up. */
+  box-shadow:
+    inset 0 1px 0 rgba(255, 255, 255, 0.25),
+    inset 0 -3px 0 rgba(0, 0, 0, 0.45),
+    0 2px 0 rgba(0, 0, 0, 0.55);
+}
+
+.interact-prompt__label {
+  padding: 0 12px;
+  font-size: 13px;
+  font-weight: 700;
+  letter-spacing: 0.02em;
   line-height: 1;
 }