fix(frank-dragoon): mount the distro XRT at the third prefix the NPU child searches

The lane's child dlopens libxrt_core.so.2 from /opt/xilinx/lib/<multiarch>/
as well; our mounts filled only /opt/xilinx/xrt/lib and the install path.
Since the host's libxrt2 was reconfigured 2026-10-20 the child dies naming
the missing prefix ('No such library
/opt/xilinx/lib/x86_64-linux-gnu/libxrt_core.so.2') and the engine
supervisor takes the WHOLE container down on a dead lane — measured
2026-10-21: frank-dragoon boot-looped 88 times with chat dead while the
GPU lines looked healthy.

Each XRT library now mounts THREE times from the same real file (never a
symlink); the multiarch name derives from FRANK_DRAGOON_XRT_DIR's basename
so the bats fixture proves the derivation. Proven end-to-end before commit:
production-shaped scratch boot + the three extra mounts answers the full
boot ledger, npu_api buckets u0..u9, and /health ok at the 262144 ceiling.

A dead lane is not survivable on this engine — arm it only with all three
prefixes (page law updated).

scripts/frank-dragoon.env

@@ -114,10 +114,13 @@ HALOGEN_NPU_MODELS=qwen3-embedding-0.6b
 FRANK_DRAGOON_NPU_DIR=/home/dank/models/halogen-v2-abliterated/npu
 # Node paths and the XRT directory are variables so the bats seam can drive
 # these gates on a box with no NPU. Ubuntu's distro XRT (libxrt2 + libxrt-npu2)
-# is mounted FILE BY FILE and TWICE EACH — once where the image looks for XRT,
-# once at its own path, because those libraries find each other at their install
-# path; the vendor forbids mounting an /opt/xilinx/xrt of symlinks into the
-# system dir, which dangle inside the container.
+# is mounted FILE BY FILE and THREE TIMES EACH — where the image looks for XRT
+# (/opt/xilinx/xrt/lib), at its own path (those libraries find each other at
+# their install path), and at /opt/xilinx/lib/<multiarch>/ (the NPU child
+# searches that third prefix; without it the lane dies naming it and the
+# supervisor takes the container down — 2026-10-21 boot loop). The basename of
+# this directory IS the multiarch name. The vendor forbids mounting an
+# /opt/xilinx/xrt of symlinks into the system dir, which dangle in the container.
 FRANK_DRAGOON_DEV_ACCEL=/dev/accel/accel0
 FRANK_DRAGOON_XRT_DIR=/usr/lib/x86_64-linux-gnu
 # sysfs root the fabric-clock preflight reads (same knob the vendor's