fix android thumbnail cache invalidation

[zerox80]

summary

this fixes stale thumbnails on android when an image gets replaced but the old cached bitmap is still around.

the thumbnail url now uses a proper cache token order:

explicit etag, then remote etag, then etag, then blank

also updated the android save paths that learn a fresh server etag after download or upload, so they persist it into both etag and remoteEtag.

details

• keep the existing coil cache setup
• make remoteEtag the main thumbnail cache token when available
• save download etags into both local etag fields
• resolve upload etags with one metadata read if the upload result is blank
• update existing db rows for content uri uploads instead of inserting folder-list rows
• preserve a usable remoteEtag when copying files

testing

• ./gradlew :opencloudApp:testOriginalDebugUnitTest --tests "eu.opencloud.android.presentation.thumbnails.ThumbnailsRequesterTest"
• ./gradlew :opencloudData:compileDebugAndroidTestKotlin
• git diff --check