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/test.md

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+# test
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+- 1
+- 2
+
+
+
+!!include path:test2.md