fix(deploy): the dragoon gate reads the deployer's own payload-dir twin

The containment gate added in #44 parsed scripts/frank-dragoon.env through a
$CHECKOUT variable that does not exist in deploy-remote.sh, so the very next
deploy died at `set -u` before it touched the unit:

  ./scripts/deploy-remote.sh: line 1445: CHECKOUT: unbound variable

deploy-remote.sh runs from the checkout root and every other path in that block
is a parity-twin default (LLM_DRAGOON_CKPT/_VISION/_TOK_DIR), so the payload dir
gets the same treatment: LLM_DRAGOON_MODEL_DIR, defaulted to the deployed path,
compared directly. The seam now asserts that twin against the env file next to
the NPU twins it already checks, and the containment comparison itself is
verified both ways (inside accepted; the old outside path and a shared-prefix
sibling both refused).

tests/frank_dragoon_unit.bats

@@ -357,6 +357,9 @@ $(cat "$TEST_TMP/serve.log")"
     npu_models="$(sed -nE 's/^HALOGEN_NPU_MODELS=(.*)$/\1/p' "$ENV_FILE")"
     grep -qF "LLM_DRAGOON_NPU_DIR=\"\${LLM_DRAGOON_NPU_DIR:-$npu_dir}\"" "$DEPLOYER"
     grep -qF "LLM_DRAGOON_NPU_MODELS=\"\${LLM_DRAGOON_NPU_MODELS:-$npu_models}\"" "$DEPLOYER"
+    # The deployer's own copy of the payload dir is what the lane's containment
+    # gate compares against — a stale twin would wave a bad staging path through.
+    grep -qF "LLM_DRAGOON_MODEL_DIR=\"\${LLM_DRAGOON_MODEL_DIR:-$dir}\"" "$DEPLOYER"
     net="$(sed -nE 's/^FRANK_DRAGOON_NETWORK=(.*)$/\1/p' "$ENV_FILE")"
     grep -qF "LLM_DRAGOON_NETWORK=\"\${LLM_DRAGOON_NETWORK:-$net}\"" "$DEPLOYER"
 }