fix(phase4): make Linux acceptance failures legible (#76)

Many Linux acceptance checks are bare `[[ ... ]]` or `--quiet` assertions that
exit non-zero with no output. When one fails, the only signal is "Process
completed with exit code 1" with no indication of which check failed, forcing a
full candidate rerun to learn anything. Add an ERR trap that prints the exact
line number and failing command as a GitHub error annotation, so a failing
candidate is diagnosable from the log alone.

No behavior change on success; existing guarded checks keep their own messages.

Co-authored-by: Joseph Yaksich <gitcommit90@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: gitcommit90

ops/platform-acceptance/linux.sh

@@ -1,6 +1,12 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# Many acceptance checks are bare `[[ ... ]]` or `--quiet` assertions that exit
+# non-zero with no output, so a failure surfaces only as "exit code 1" with no
+# clue which check failed. Report the exact line and command instead, so a
+# failing candidate is diagnosable from the log alone rather than by rerunning.
+trap 'status=$?; echo "::error::Linux acceptance failed at line ${LINENO} (exit ${status}): ${BASH_COMMAND}" >&2' ERR
+
 ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
 ARCHIVE="${HELM_CANDIDATE_ARCHIVE:?exact Linux candidate archive is required}"
 OFFLINE_ARCHIVE="${HELM_CANDIDATE_OFFLINE_ARCHIVE:?exact Linux offline candidate archive is required}"