feat: Enhance WebDAV file management and UI

- Add functionality to create new collections via API
- Implement copy and move operations between collections
- Improve image rendering in markdown preview with relative path resolution
- Add support for previewing binary files (images, PDFs)
- Refactor modal styling to use flat buttons and improve accessibility

collections/7madah/tests/sub_tests/file1.md

@@ -0,0 +1,22 @@
+# Start to end file
+
+### Graph
+
+---
+
+This is just for testing
+
+---
+
+**See what i did?**
+
+---
+
+```mermaid
+graph TD
+    A[Start] --> B{Process};
+    B --> C{Decision};
+    C -- Yes --> D[End Yes];
+    C -- No --> E[End No];
+```
+