fix(core,fuse,gui): date photos by their EXIF when nothing else does

A Takeout photo with no sidecar and no date in its name was filed under
the day of the import, and the app dated uploads by modification time.
A new `exiftime` module reads DateTimeOriginal (then DateTimeDigitized)
with its offset. Takeout uses it for undated photos it copies out for a
thumbnail, and the daemon uses it for app uploads before falling back to
the modification time (B244).

crates/pdfs-core/Cargo.toml

@@ -30,3 +30,4 @@ async-trait.workspace = true
 libc.workspace = true
 zeroize.workspace = true
 base64.workspace = true
+exif = { version = "0.6", package = "kamadak-exif" }