Restructure frontend code to allow for extensions (#4721)

# Description of Changes
Move frontend code into `core` folder and add infrastructure for
`proprietary` folder to include premium, non-OSS features

frontend/src/core/components/shared/HoverActionMenu.module.css

@@ -0,0 +1,28 @@
+/* Base Hover Menu */
+.hoverMenu {
+  position: absolute;
+  left: 50%;
+  transform: translateX(-50%);
+  display: flex;
+  gap: 8px;
+  align-items: center;
+  background: var(--bg-toolbar);
+  border: 1px solid var(--border-default);
+  padding: 6px 12px;
+  border-radius: 20px;
+  box-shadow: var(--shadow-md);
+  z-index: 30;
+  white-space: nowrap;
+  pointer-events: auto;
+  transition: opacity 0.2s ease-in-out;
+}
+
+/* Inside positioning (Page Editor style) - within container */
+.inside {
+  bottom: 8px;
+}
+
+/* Outside positioning (File Editor style) - below container */
+.outside {
+  bottom: -8px;
+}