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).

serverAppConfigs-docs/LLM/frank-dragoon.md

@@ -256,9 +256,14 @@ lane is **armed and serving** since 2026-10-19 (`HALOGEN_NPU_MODELS=qwen3-embedd
    (`dankclaw/udev/98-halogen-npu-access.rules`, installed and re-triggered by the deployer, `0666` like the GPU
    compute nodes beside it); the serve script refuses any node that is not other-accessible, so the fault cannot
    return as a crash-loop.
-2. The host's XRT reachable inside: there is **no `/opt/xilinx/xrt`** here — distro packages put the three files the
-   container needs (`libxrt_coreutil.so.2`, `libxrt_core.so.2`, `libxrt_driver_xdna.so.2`) in
-   `/usr/lib/x86_64-linux-gnu`, where all three exist.
+2. The host's XRT reachable inside, at **THREE prefixes per library**: there is **no `/opt/xilinx/xrt`** here —
+   distro packages put the three files the container needs (`libxrt_coreutil.so.2`, `libxrt_core.so.2`,
+   `libxrt_driver_xdna.so.2`) in `/usr/lib/x86_64-linux-gnu`. The serve script mounts each REAL file (never a
+   symlink) at `/opt/xilinx/xrt/lib/`, at its own path, AND at `/opt/xilinx/lib/<multiarch>/` — the NPU child
+   searches that third prefix and a missing one is fatal: since the host's `libxrt2` was reconfigured
+   2026-10-20 the child died with `No such library '/opt/xilinx/lib/x86_64-linux-gnu/libxrt_core.so.2'` and the
+   engine supervisor took the WHOLE container down on it (88-restart loop, chat dead beside a healthy GPU line).
+   A dead lane is not survivable here — arm the lane only with all three prefixes mounted.
 3. **The GPU fabric clock held at its top level, or the engine refuses to start.** GPU and NPU work share the die:
    while `pp_dpm_fclk` is changing speed, concurrent GPU work can hang the machine and corrupt NPU results. The
    engine holds the clock itself only when it runs as root with `/sys` mounted; `frank-dragoon` is a **rootless**