fix: show LXC storage in --dry-run summary

The LXC storage check runs in every mode, but its results were never
printed in the --dry-run summary, so a --dry-run appeared to skip LXC
storage entirely. Add an "LXC Storage:" section to the summary
(per-container usage %, a warning flag over the LXC_WARNING threshold, and
the issue count) via a small, testable helper `_format_lxc_dry_run()`.
Adds 4 regression tests.

Closes #23
Ref: #23

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_hwmon.py

@@ -503,3 +503,36 @@ class TestAttributeThresholds:
         """Age is still *tracked* (just not ticketed) — new-drive detection must work."""
         assert monitor._is_new_drive(100) is True      # ~4 days
         assert monitor._is_new_drive(64860) is False   # ~7.4 years
+
+
+# ── _format_lxc_dry_run (LXC storage shown in --dry-run summary; issue #23) ────
+
+class TestLxcDryRunSummary:
+    def test_includes_container_usage_and_flags_over_threshold(self, monitor):
+        """Regression for issue #23: dry-run summary must surface LXC storage."""
+        lxc = {
+            'status': 'WARNING',
+            'issues': ['LXC 105 high storage usage: 84.0% on /'],
+            'containers': [
+                {'vmid': '105', 'filesystems': [{'mountpoint': '/', 'usage_percent': 84.0}]},
+            ],
+        }
+        text = '\n'.join(monitor._format_lxc_dry_run(lxc))
+        assert 'LXC Storage:' in text
+        assert 'CT105 /' in text and '84.0% used' in text
+        assert '⚠️' in text               # flagged: over the 80% warning threshold
+        assert 'Issues: 1 found' in text
+
+    def test_healthy_container_not_flagged(self, monitor):
+        lxc = {'status': 'OK', 'issues': [],
+               'containers': [{'vmid': '119', 'filesystems': [{'mountpoint': '/', 'usage_percent': 26.0}]}]}
+        text = '\n'.join(monitor._format_lxc_dry_run(lxc))
+        assert 'CT119 /' in text and '26.0% used' in text
+        assert '⚠️' not in text
+
+    def test_empty_when_no_containers(self, monitor):
+        assert monitor._format_lxc_dry_run({'status': 'OK', 'containers': [], 'issues': []}) == []
+
+    def test_error_status_is_reported(self, monitor):
+        lines = monitor._format_lxc_dry_run({'status': 'ERROR', 'containers': [], 'issues': ['boom']})
+        assert any('check error' in ln for ln in lines)