fix(irv-ml1): self-heal the gcc-11/gfortran-12 -lgfortran mismatch for soundgen

Default gcc is gcc-11 (CUDA/torch R14 pin) but the only gfortran is 12,
whose libgfortran-12-dev puts the unversioned libgfortran.so only in the
gcc-12 dir. R links shared objects with gcc-11 + -lgfortran, so the whole
Fortran dependency chain (quadprog/tseries/RcppArmadillo -> soundgen) failed
'cannot find -lgfortran'. Adds an idempotent step installing libgfortran-11-dev
(guarded on 'gcc -print-file-name=libgfortran.so' not resolving). Additive;
default toolchain untouched.

playbooks/irv-ml1-r15-r16-sudo.yaml

@@ -34,6 +34,18 @@ steps:
       libcurl4-openssl-dev libssl-dev libxml2-dev
     when: "! command -v Rscript >/dev/null 2>&1"
 
+  # gcc/gfortran version mismatch fix. irv-ml1's default `gcc` is gcc-11
+  # (deliberate — the CUDA/torch R14 stack pins it), but the only gfortran is
+  # gfortran-12, whose libgfortran-12-dev puts the unversioned `libgfortran.so`
+  # ONLY in the gcc-12 dir. R links shared objects with SHLIB_LD=$(CC)=gcc-11 +
+  # `-lgfortran`, so every Fortran package (quadprog→tseries→soundgen, etc.)
+  # fails "cannot find -lgfortran". libgfortran-11-dev adds the symlink to the
+  # gcc-11 dir. Additive — does NOT change the default toolchain.
+  - name: Ensure the default gcc's Fortran link lib resolves (gcc-11 here)
+    sudo: true
+    shell: DEBIAN_FRONTEND=noninteractive apt-get install -y libgfortran-11-dev
+    when: "! gcc -print-file-name=libgfortran.so | grep -q /"
+
   - name: Pin the Ollama service to the A6000 (UUID) via systemd drop-in
     sudo: true
     shell: |