fix(webdav): stop the resolution ladder at 2048

The largest rung is the largest box a generator is asked for, and fill and stretch enlarge a small source to fill it, so the rungs above 2048 let a tiny image cost whatever 8K costs. Web asks for 1200 at most.

services/webdav/README.md

@@ -30,9 +30,9 @@ The following query parameters are supported:
 
 #### Thumbnail Resolution
 
-`WEBDAV_THUMBNAIL_RESOLUTIONS` is a ladder of edge lengths, not a list of boxes. Each axis of a request is rounded up to the next length on the ladder, on its own, so a thumbnail never comes back in a different orientation than it was asked for. The largest length is the cap: a request above it, and an axis left unconstrained, get that one.
+`WEBDAV_THUMBNAIL_RESOLUTIONS` is a ladder of edge lengths, not a list of boxes. Its largest entry is also the largest thumbnail this service asks a generator for, which is why it tops out at 2048: `fill` and `stretch` enlarge a small source to fill the box, so a higher rung lets a tiny image cost whatever that box costs. Each axis of a request is rounded up to the next length on the ladder, on its own, so a thumbnail never comes back in a different orientation than it was asked for. The largest length is the cap: a request above it, and an axis left unconstrained, get that one.
 
-Example with the default ladder (16, 32, 64, 128, 192, 256, 320, 384, 448, 512, 640, 768, 1024, 1280, 1920, 2560, 3840, 7680):
+Example with the default ladder (16, 32, 64, 128, 192, 256, 320, 384, 448, 512, 640, 768, 1024, 1280, 1920, 2048):
 
 Requested: 18x12\
 Returned: 32x16

services/webdav/pkg/config/defaults/defaultconfig.go

@@ -49,7 +49,7 @@ func DefaultConfig() *config.Config {
 		ThumbnailCacheBackend:     "file",
 		ThumbnailResolutions: []string{
 			"16", "32", "64", "128", "192", "256", "320", "384", "448",
-			"512", "640", "768", "1024", "1280", "1920", "2560", "3840", "7680",
+			"512", "640", "768", "1024", "1280", "1920", "2048",
 		},
 	}
 }