feat(ui): implement smooth Apple-style spring animation for toggle switch

Motivation:
The previous toggle switch animation was abrupt and rigid. The clickable area also spanned the entire row width, which led to unintentional clicks.

Implementation:
- CSS: Replaced static transitions with cubic-bezier spring physics, hardware-accelerated transforms (translate), and pressed-state squish feedback.
- JS: Wrapped the switch in a constrained flex container, replacing the full-width <label> wrapper to fix the clickable area.

web/css/provider_manager.css

@@ -473,59 +473,81 @@
 }
 
 /* ============================================================
-   SWITCH / TOGGLE
+   SWITCH / TOGGLE — Ultra-smooth Apple-style spring animation
    ============================================================ */
 .llm-pm-switch {
     position: relative;
     display: inline-block;
-    width: 42px;
-    height: 22px;
+    width: 44px;
+    height: 24px;
+    flex-shrink: 0;
+    cursor: pointer;
 }
 
 .llm-pm-switch input {
     opacity: 0;
     width: 0;
     height: 0;
+    position: absolute;
 }
 
 .llm-pm-slider {
     position: absolute;
-    cursor: pointer;
-    top: 0;
-    left: 0;
-    right: 0;
-    bottom: 0;
-    background-color: rgba(255, 255, 255, 0.08);
-    transition: var(--glass-transition);
-    border-radius: 22px;
-    border: 1px solid var(--glass-border);
-    box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.3);
+    inset: 0;
+    border-radius: 24px;
+    border: 1.5px solid rgba(255, 255, 255, 0.1);
+    background-color: rgba(255, 255, 255, 0.1);
+    box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.35);
+    transition:
+        background-color 0.35s cubic-bezier(0.4, 0, 0.2, 1),
+        border-color 0.35s cubic-bezier(0.4, 0, 0.2, 1),
+        box-shadow 0.4s cubic-bezier(0.4, 0, 0.2, 1);
+    will-change: background-color;
 }
 
+/* The thumb (white circle) — spring physics */
 .llm-pm-slider:before {
-    position: absolute;
     content: "";
-    height: 16px;
-    width: 16px;
+    position: absolute;
+    height: 18px;
+    width: 18px;
     left: 2px;
-    bottom: 2px;
-    background-color: var(--glass-text-secondary);
-    transition: var(--glass-transition);
+    top: 50%;
+    transform: translateY(-50%) translateX(0px);
+    background: rgba(200, 200, 210, 0.9);
     border-radius: 50%;
-    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
+    box-shadow: 0 1px 4px rgba(0, 0, 0, 0.4), 0 0 0 0.5px rgba(0, 0, 0, 0.15);
+    /* cubic-bezier(0.34, 1.56, 0.64, 1): fast shoot, slight overshoot, then settle — the "Apple spring" */
+    transition:
+        transform 0.38s cubic-bezier(0.34, 1.56, 0.64, 1),
+        width 0.18s cubic-bezier(0.4, 0, 0.2, 1),
+        background 0.25s ease;
+    will-change: transform;
 }
 
+/* Checked (ON) state */
 .llm-pm-switch input:checked+.llm-pm-slider {
-    background: linear-gradient(135deg, var(--glass-accent), #8b5cf6);
+    background-color: var(--glass-accent);
     border-color: transparent;
-    box-shadow: 0 0 12px var(--glass-accent-glow),
+    box-shadow:
+        0 0 0 3px rgba(99, 102, 241, 0.18),
+        0 0 14px rgba(99, 102, 241, 0.4),
         inset 0 1px 2px rgba(255, 255, 255, 0.15);
 }
 
 .llm-pm-switch input:checked+.llm-pm-slider:before {
-    transform: translateX(20px);
-    background-color: white;
-    box-shadow: 0 1px 4px rgba(0, 0, 0, 0.25);
+    transform: translateY(-50%) translateX(20px);
+    background: white;
+    box-shadow: 0 1px 5px rgba(0, 0, 0, 0.3);
+}
+
+/* Press feedback — thumb squishes horizontally on mousedown */
+.llm-pm-switch:active .llm-pm-slider:before {
+    width: 22px;
+}
+
+.llm-pm-switch:active input:checked+.llm-pm-slider:before {
+    transform: translateY(-50%) translateX(18px);
 }
 
 /* ============================================================

web/js/provider_manager.js

@@ -911,7 +911,7 @@ class ProviderManager {
         // Build DOM
         const fields = [
             $el("div.llm-pm-field", [
-                $el("label", [
+                $el("div", { style: { display: "flex", justifyContent: "space-between", alignItems: "center", fontSize: "0.8em", fontWeight: "600", color: "var(--glass-text-secondary)", textTransform: "uppercase", letterSpacing: "0.06em", marginBottom: "8px" } }, [
                     $el("span", t("provider_name")),
                     $el("div", { style: { display: "flex", alignItems: "center", gap: "8px" } }, [
                         $el("span", { style: { fontSize: "0.8em", fontWeight: "normal" } }, t("enable_nodes")),