feat(theme): update homepage with Apple-style design and add footer

- Change hero button from "Course Outline" to "GitHub" linking to repository
- Update color scheme to Apple blue gradient and refine button styles
- Add Apple-style footer with localized content, breadcrumb, and policy links
- Introduce top promotional banner with localized call-to-action
- Improve responsive design and adjust spacing for better visual hierarchy

docs/.vitepress/theme/style.css

@@ -4,6 +4,10 @@
   --vp-sidebar-nav-section-gap: 8px;
   --ev-doc-font-size: 14px;
   --ev-doc-line-height: 1.65;
+  --vp-c-brand-1: #0071e3;
+  --vp-c-brand-2: #0077ed;
+  --vp-c-brand-3: #0066cc;
+  --vp-c-brand-soft: rgba(0, 113, 227, 0.14);
 }
 
 .vp-doc {
@@ -302,42 +306,47 @@
 
 /* Hero Section Refinements */
 .VPHomeHero .name {
-  background: -webkit-linear-gradient(315deg, #42d392 25%, #647eff);
+  background: -webkit-linear-gradient(315deg, #0071e3 10%, #5ac8fa 90%);
   background-clip: text;
   -webkit-background-clip: text;
   -webkit-text-fill-color: transparent;
-  filter: drop-shadow(0 0 30px rgba(66, 211, 146, 0.3));
+  filter: drop-shadow(0 0 24px rgba(0, 113, 227, 0.28));
 }
 
 .VPHomeHero .text {
-  font-weight: 500;
-  color: var(--vp-c-text-2);
+  font-weight: 600;
+  color: #1d1d1f;
+  letter-spacing: -0.02em;
 }
 
 .VPHomeHero .action .VPButton.brand {
-  border-radius: 20px;
-  background-image: linear-gradient(to right, #42d392, #647eff);
+  border-radius: 999px;
+  background-image: none;
+  background-color: #0071e3;
   border: none;
+  box-shadow: none;
   transition:
     transform 0.2s,
     opacity 0.2s;
 }
 
 .VPHomeHero .action .VPButton.brand:hover {
-  transform: scale(1.05);
-  opacity: 0.9;
+  transform: scale(1.02);
+  background-color: #0077ed;
+  opacity: 1;
 }
 
 .VPHomeHero .action .VPButton.alt {
-  border-radius: 20px;
-  border-color: var(--vp-c-divider);
-  background-color: var(--vp-c-bg-soft);
+  border-radius: 999px;
+  border-color: #d2d2d7;
+  background-color: #fff;
+  color: #1d1d1f;
   transition: transform 0.2s;
 }
 
 .VPHomeHero .action .VPButton.alt:hover {
-  transform: scale(1.05);
-  background-color: var(--vp-c-bg);
+  transform: scale(1.02);
+  background-color: #f5f5f7;
 }
 
 /* HomeFeatures Sections Scroll Offset */