feat: implement split button dropdown for install options

- Replace separate VS Code/Insiders buttons with single Install dropdown
- Primary 'Install' button opens in VS Code, dropdown chevron reveals options
- Dropdown shows 'VS Code' and 'VS Code Insiders' choices
- Add CSS for split button styling with glassmorphism dropdown
- Apply to modal and all list views (agents, prompts, instructions)

website/public/data/manifest.json

@@ -1,5 +1,5 @@
 {
-  "generated": "2026-01-28T08:51:25.860Z",
+  "generated": "2026-01-28T22:33:37.643Z",
   "counts": {
     "agents": 140,
     "prompts": 134,

website/public/styles/global.css

@@ -646,6 +646,101 @@ a:hover {
   color: var(--color-text);
 }
 
+/* Split Button Dropdown */
+.install-dropdown {
+  position: relative;
+  display: inline-flex;
+}
+
+.install-dropdown .install-btn-main {
+  border-top-right-radius: 0;
+  border-bottom-right-radius: 0;
+  border-right: 1px solid rgba(255, 255, 255, 0.2);
+}
+
+.install-dropdown .install-btn-toggle {
+  border-top-left-radius: 0;
+  border-bottom-left-radius: 0;
+  padding: 10px 10px;
+  min-width: auto;
+}
+
+.install-dropdown .install-btn-toggle svg {
+  transition: transform var(--transition);
+}
+
+.install-dropdown.open .install-btn-toggle svg {
+  transform: rotate(180deg);
+}
+
+.install-dropdown-menu {
+  position: absolute;
+  top: 100%;
+  right: 0;
+  margin-top: 4px;
+  min-width: 160px;
+  background: var(--color-bg-secondary);
+  border: 1px solid var(--color-border);
+  border-radius: var(--border-radius);
+  box-shadow: var(--shadow-md);
+  z-index: 1000;
+  opacity: 0;
+  visibility: hidden;
+  transform: translateY(-8px);
+  transition: all var(--transition);
+}
+
+.install-dropdown.open .install-dropdown-menu {
+  opacity: 1;
+  visibility: visible;
+  transform: translateY(0);
+}
+
+.install-dropdown-menu a {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 10px 14px;
+  color: var(--color-text);
+  text-decoration: none;
+  font-size: 14px;
+  transition: background var(--transition);
+}
+
+.install-dropdown-menu a:first-child {
+  border-radius: var(--border-radius) var(--border-radius) 0 0;
+}
+
+.install-dropdown-menu a:last-child {
+  border-radius: 0 0 var(--border-radius) var(--border-radius);
+}
+
+.install-dropdown-menu a:hover {
+  background: var(--color-bg-tertiary);
+}
+
+.install-dropdown-menu svg {
+  width: 16px;
+  height: 16px;
+  flex-shrink: 0;
+}
+
+/* Small variant for list items */
+.install-dropdown.install-dropdown-small .install-btn-main {
+  padding: 8px 12px;
+  font-size: 13px;
+}
+
+.install-dropdown.install-dropdown-small .install-btn-toggle {
+  padding: 8px 8px;
+}
+
+.install-dropdown-menu .dropdown-divider {
+  height: 1px;
+  background: var(--color-border);
+  margin: 4px 0;
+}
+
 /* Spinner animation */
 @keyframes spin {
   from {