ci: drop host nasm install — mcpp >= 0.0.95 self-bootstraps nasm

mcpp resolves nasm like any toolchain: PATH first, then the mcpp sandbox,
then an automatic 'xlings install nasm', lazily and only when the build
plan actually contains .asm units (compat.ffmpeg). The sandbox copy lives
under ~/.mcpp/registry, so the CI cache carries it across runs. Keeping a
host apt install would mask the self-bootstrap path this repo is supposed
to exercise.

Author: speak-agent

.github/workflows/validate.yml

@@ -211,13 +211,11 @@ jobs:
             echo "MCPP_VENDORED_XLINGS=$root/${{ matrix.xlings }}" >> "$GITHUB_ENV"
             echo "$root/bin" >> "$GITHUB_PATH"
           fi
-      # compat.ffmpeg carries NASM .asm sources; mcpp resolves nasm PATH-first
-      # (ubuntu-24.04 ships nasm 2.16 — deterministic, no index round-trip).
-      - name: Install nasm (Linux)
-        if: runner.os == 'Linux'
-        shell: bash
-        run: sudo apt-get update && sudo apt-get install -y nasm
-
+      # compat.ffmpeg carries NASM .asm sources. No host install needed:
+      # mcpp >= 0.0.95 resolves nasm itself (PATH → sandbox → auto
+      # `xlings install nasm`), lazily, only when the plan has .asm units —
+      # same self-bootstrap contract as the llvm toolchain. The sandbox copy
+      # lands in ~/.mcpp/registry, so the cache carries it across runs.
       - name: mcpp test --workspace
         shell: bash
         env: