drone: recipe-ci step uses HOME=/root so abra finds /root/.abra config

The exec runner sets HOME to a per-build workspace, leaving ~/.abra empty
(FATA directory is empty: .../home/drone/.abra/servers). Force HOME=/root in the
step so abra and the harness's ~/.abra/recipes resolve to the real config, as the
manual runs did. Safe at capacity=1 (no concurrent build shares /root/.abra).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.drone.yml

@@ -50,6 +50,10 @@ steps:
     environment:
       STAGES: install,upgrade,backup
       CCCI_JANITOR_MAX_AGE: "0"
+      # The exec runner points HOME at a per-build workspace; force it to /root so abra finds its
+      # server config + recipes under /root/.abra (as the manual M4/M5 runs did). Safe: capacity=1
+      # means no concurrent build shares /root/.abra.
+      HOME: /root
     commands:
       # RECIPE/REF/PR/SRC are injected as env vars from the build's custom params.
       - 'echo "recipe-ci: RECIPE=$RECIPE REF=$REF PR=$PR SRC=$SRC stages=$STAGES"'