fix(tests): grep -c already outputs 0 on no match, || echo "0" duplicated it

The shellcheck test captured "0\n0" instead of "0" because grep -c
outputs the count (0) even on exit code 1, then || echo "0" added
a second zero. Changed to || true.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Sw2Ti3a4Ad8U6JuAyNib1

Author: Frederik

tests/test-nightshift.sh

@@ -290,7 +290,7 @@ if command -v shellcheck &>/dev/null; then
   for script in config.sh coordinator.sh worker.sh summary.sh summary-morning.sh lesson-generator.sh install.sh; do
     TESTS_RUN=$((TESTS_RUN + 1))
     sc_output=$(shellcheck -S warning "$PROJECT_DIR/$script" 2>&1 || true)
-    sc_errors=$(echo "$sc_output" | grep -c "^In " || echo "0")
+    sc_errors=$(echo "$sc_output" | grep -c "^In " || true)
     if [[ "$sc_errors" -eq 0 ]]; then
       TESTS_PASSED=$((TESTS_PASSED + 1))
       echo -e "  ${GREEN}PASS${NC} shellcheck: $script"