oak-app: fix the NSIS license path

cargo-packager canonicalizes licenseFile relative to the crate directory
(the icons/resources entries already use ../../ for that reason), so the
NSIS bundling failed with "I/O Error (LICENSE): The system cannot find
the file specified" once the Windows packaging got that far. Point it at
../../LICENSE.

crates/oak-app/Cargo.toml

@@ -142,7 +142,7 @@ description = "Oak Video Editor"
 longDescription = "Oak Video Editor: a free, open-source non-linear video editor written in Rust."
 authors = ["Oak Team"]
 copyright = "Copyright (C) 2026 Oak Team"
-licenseFile = "LICENSE"
+licenseFile = "../../LICENSE"
 category = "Video"
 icons = ["../../icons/icon.png"]
 # The UI string tables (language packs); users can drop extra