fix: prevent default folder uploads from creating albums when not asked to

[niieani]

Issue

I'm seeing an album with an empty name created when uploading images, even when no option that indicates an album should be created (like --folder-as-album or --into-album) is added.

Here's what I see in logs:

{"time":"2025-10-13T09:12:58.989093-07:00","level":"INFO","msg":"added to an album","file":"fixture_metadata:pixel-photo/PXL_20250215_001150100.jpg","album":""}
{"time":"2025-10-13T09:12:58.995687-07:00","level":"INFO","msg":"created album","album":"","assets":2}

Root cause

• In ImportFolderCmd.RegisterFlags the default is assigned as the lowercase string "none" instead of the AlbumFolderMode constant adapters/folder/commands.go:60 Because the enum values are uppercase ("NONE", "FOLDER", "PATH"), the later check ifc.UsePathAsAlbumName != FolderModeNone evaluates true for the default, so the album-building branch always runs.
• Inside that branch the switch has no matching case, leaving Album as the empty string; nevertheless a.Albums is set to []assets.Album{{Title: ""}}, so every upload is queued for an album whose key/title is "" adapters/folder/run.go:394-431.
• The upload pipeline dutifully creates that album, yielding the added to an album and created album log lines with an empty title app/upload/run.go:533-542, app/upload/run.go:499-544.

Fix Summary

• ensure the default folder uploader album mode uses the NONE constant
• allow AlbumFolderMode to accept "none" input explicitly
• add regression tests covering the default and parser behavior

Testing

• GOCACHE=/Volumes/Projects/Software/mio/immich-go/.gocache go test ./adapters/folder -run TestRegisterFlagsSetsAlbumModeNone