frank-small: --attention-backend flag (env var removed in this build)

The VLLM_ATTENTION_BACKEND env var does not exist in this vLLM dev
build (warns 'Unknown vLLM environment variable' and is ignored), so
the pin landed nowhere and Gemma4's hook force-selected TRITON_ATTN
again. Pass --attention-backend TURBOQUANT as a CLI flag instead.

scripts/serve-frank-small.sh

@@ -44,6 +44,7 @@ fi
 : "${MAX_NUM_SEQS:=16}"
 : "${MAX_NUM_BATCHED_TOKENS:=16384}"
 : "${SPEC_NUM_TOKENS:=4}"
+: "${ATTENTION_BACKEND:=TURBOQUANT}"
 : "${ENFORCE_EAGER:=0}"
 
 # Fail loudly rather than half-loading a model into VRAM: a missing file here
@@ -66,6 +67,7 @@ VLLM_FLAGS=(
 --kv-cache-dtype "$KV_CACHE_DTYPE"
 --max-num-seqs "$MAX_NUM_SEQS"
 --max-num-batched-tokens "$MAX_NUM_BATCHED_TOKENS"
+--attention-backend "$ATTENTION_BACKEND"
 --speculative-config "$SPEC_CONFIG"
 --reasoning-parser gemma4
 --enable-auto-tool-choice