feat: frank-default-large 2x 256k context slots (CTX_SIZE=524288, PARALLEL=2)

Total KV: ~12.8 GiB (6.4 GiB per slot × 2). Model is 98.5 GiB mmap'd
into 116 GiB SVM-backed unified memory.

scripts/serve-frank-large.sh

@@ -44,8 +44,8 @@ fi
 : "${ALIAS:=frank-default-large}"
 : "${BIND_ADDR:=0.0.0.0}"
 : "${LISTEN_PORT:=7770}"
-: "${CTX_SIZE:=131072}"
-: "${PARALLEL:=1}"
+: "${CTX_SIZE:=524288}"
+: "${PARALLEL:=2}"
 : "${BATCH_SIZE:=4096}"
 : "${UBATCH_SIZE:=4096}"
 : "${NUM_THREADS:=16}"