refactor: standardise S3 URL generation (#362)

* refactor: replace presigned URL uploads with backend upload endpoints

* feat: update avatar upload to use new endpoint

* refactor: use createS3Client in auth hooks

* feat: generate presigned URLs for avatars

* fix: show avatar image in user menu

* fix: hide tooltip if content is empty

* fix: support external avatar URLs in generateAvatarUrl

* fix: remove content type restriction on attachments

packages/shared/package.json

@@ -36,6 +36,8 @@
   },
   "prettier": "@kan/prettier-config",
   "dependencies": {
+    "@aws-sdk/client-s3": "^3.802.0",
+    "@aws-sdk/s3-request-presigner": "^3.812.0",
     "date-fns": "^4.1.0",
     "jose": "^6.1.2",
     "nanoid": "^5.0.9",