Card: note the litert-lm 0.15 ExecutorMetadata update (weights unchanged)

Add ExecutorMetadata section required by litert-lm >= 0.15 (weights unchanged; still runs on 0.14)

Add ExecutorMetadata section required by litert-lm >= 0.15 (weights unchanged; still runs on 0.14)

LFM2.5-1.2B-Instruct LiteRT-LM: int8 (GSM8K 81%, bf16 parity) + int4 (736MB, 1.7x faster decode on-device); CPU backend; conv-state prefill fix baked into export

initial commit