Implement version 0.0.3 features

- Add file attachment support for product versions (Media Library)
- Add version auto-detection from uploaded filenames
- Implement secure customer downloads with hash verification
- Add license key copy-to-clipboard functionality
- Redesign customer licenses page with card-based UI
- Fix product versions meta box visibility for non-licensed types
- Add DownloadController for secure file delivery
- Update CLAUDE.md roadmap and session history

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

assets/css/admin.css

@@ -145,3 +145,23 @@
     font-style: italic;
     color: #666;
 }
+
+/* File Upload UI */
+.selected-file-name {
+    display: inline-block;
+    margin-right: 10px;
+    padding: 5px 10px;
+    background: #e7f3ff;
+    border-radius: 3px;
+    font-weight: 500;
+}
+
+.selected-file-name:empty {
+    display: none;
+}
+
+#versions-table .dashicons-media-archive {
+    color: #2271b1;
+    vertical-align: middle;
+    margin-left: 5px;
+}