Add ZIP bulk upload to asset manager

Features:
- Upload ZIP files with folder structure
- Automatic extraction and MD5/SHA256 calculation
- Preserve folder paths as EA CDN paths
- Auto-categorize based on file extensions
- Update existing assets automatically
- Bootstrap tabs for single/bulk upload UI
- Progress feedback (X new, Y updated)

Example: cars/porsche.dat → /cars/porsche.dat

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

RR3CommunityServer/obj/Debug/net8.0/RR3CommunityServer.sourcelink.json

@@ -1 +1 @@
-{"documents":{"E:\\rr3\\RR3CommunityServer\\*":"https://raw.githubusercontent.com/ssfdre38/rr3-server/f1d0d43cb70abf0fc44598a01a6250f3b7b73922/*"}}
+{"documents":{"E:\\rr3\\RR3CommunityServer\\*":"https://raw.githubusercontent.com/ssfdre38/rr3-server/15e842ce855b748cc97c43261eba408067128330/*"}}