feat(aigc): implement travel AIGC feature and clean up legacy assets

- Replace all local static AIGC assets with OSS hosted URLs to reduce bundle size
- Add travelAIGC command to ChatModel and update quick access menu to link to AIGC home
- Implement AIGC user consent flow with local storage persistence for compliance
- Refactor Discovery page layout, remove unused HeritageDiscoverySection component
- Update ChatTopNavBar to support dynamic navigation bar height based on system info
- Restructure ChatMainList layout for better discovery panel interaction
- Remove deprecated local asset files and clean up unused imports across codebase

src/pages/ChatMain/ChatMainList/styles/index.scss

@@ -5,23 +5,41 @@
   overscroll-behavior-y: contain;
 }
 
-.home-welcome-collapse {
-  width: 100%;
-  height: 92px;
-  flex-shrink: 0;
+.discovery-shell {
+  position: relative;
+  flex-basis: 0;
+  height: 0;
+  min-height: 0;
   overflow: hidden;
-  opacity: 1;
-  transform: translateY(0);
-  transition:
-    height 240ms ease,
-    opacity 240ms ease,
-    transform 240ms ease;
+  background: $theme-color-50;
 }
 
-.home-welcome-collapse.is-collapsed {
-  height: 0;
-  opacity: 0;
-  transform: translateY(-8px);
+.home-welcome-panel {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  z-index: 1;
+  width: 100%;
+  height: 92px;
+  overflow: hidden;
+}
+
+.discovery-panel {
+  position: absolute;
+  top: 92px;
+  right: 0;
+  bottom: 0;
+  left: 0;
+  z-index: 2;
+  min-height: 0;
+  overflow: hidden;
+  background: $theme-color-50;
+  transition: top 240ms ease;
+}
+
+.discovery-panel.is-collapsed {
+  top: 0;
 }
 
 .home-hero {