Add iOS Background Assets manifest v1

Remove unused int4 small variant (medium-only)

medium = no-sparse 8-bit palettized ivrit-large-v3-turbo (~888MB; replaces sparse)

Remove old sparse medium before replacing with no-sparse

Remove temp medium-v2 (folding no-sparse model into medium)

Add medium-v2: no-sparse 8-bit palettized ivrit-large-v3-turbo (beats sparse medium on WER, smaller)

Initial commit