Fix qmake shader output path

[DavDood]

Fixed qmake shader baker output paths so generated .qsb files stay under app/shaders. This prevents qmake from creating a stray ../app/shaders/shaders directory outside the repository.

Verification

• Regenerated app/Makefile and confirmed qsb targets no longer reference ../../app/shaders.
• Removed the stray parent app directory and ran make -j8.
• Confirmed the parent app directory was not recreated.