Tighten Gemini expansion and unify crop slider

frontend/index.html

@@ -96,14 +96,16 @@
                 <span id="rangeSummary">00:00:00 - 00:00:00</span>
               </div>
               <div class="space-y-3">
-                <label class="block space-y-2">
-                  <span class="text-xs uppercase tracking-[0.2em] text-zinc-500">Start</span>
-                  <input id="startRange" type="range" min="0" max="0" value="0" step="1" class="slider-thumb w-full appearance-none bg-transparent" />
-                </label>
-                <label class="block space-y-2">
-                  <span class="text-xs uppercase tracking-[0.2em] text-zinc-500">End</span>
-                  <input id="endRange" type="range" min="0" max="0" value="0" step="1" class="slider-thumb w-full appearance-none bg-transparent" />
-                </label>
+                <div class="dual-slider relative h-10">
+                  <div class="dual-slider__track absolute left-0 right-0 top-1/2 h-1 -translate-y-1/2 rounded-full bg-white/15"></div>
+                  <div id="rangeFill" class="dual-slider__fill absolute top-1/2 h-1 -translate-y-1/2 rounded-full bg-white"></div>
+                  <button id="startThumb" type="button" class="dual-slider__thumb absolute top-1/2 h-5 w-5 -translate-y-1/2 rounded-full border-2 border-zinc-950 bg-white"></button>
+                  <button id="endThumb" type="button" class="dual-slider__thumb absolute top-1/2 h-5 w-5 -translate-y-1/2 rounded-full border-2 border-zinc-950 bg-white"></button>
+                </div>
+                <div class="flex items-center justify-between text-xs uppercase tracking-[0.2em] text-zinc-500">
+                  <span id="startLabel">Start 00:00:00</span>
+                  <span id="endLabel">End 00:00:00</span>
+                </div>
               </div>
               <div class="mt-3 flex gap-3">
                 <button id="setStartFromPreview" type="button" class="flex-1 rounded-2xl border border-white/10 px-4 py-3 text-sm text-zinc-200 transition hover:border-white/30">Set Start</button>