fix(ansible): surface run failure reason; widget audit cleanup

Run UX: when start_run throws before/around launch (e.g. ENOSPC creating the
temp dir — the box is out of disk), the run was marked "failed" with empty
output. Now the exception is broadcast + written to the run output/results so
the run view shows e.g. "[run error] OSError: [Errno 28] No space left on
device" instead of a blank failure.

Widget audit follow-ups (no broken links were found; these are consistency):
- host_resource_history widget now charts root (/) disk, consistent with the
  host panel (was the opaque "disk worst").
- host_resources widget: tooltip on the health dot explaining it warns on the
  worst mount while the number shows root.
- status_overview widget detail_url /status → /status/ (avoid redirect).
- Normalize ad-hoc widget empty-states to the shared .empty style (wording,
  which distinguishes "configured" vs "data yet", preserved).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/host_agent/templates/widget_history.html

@@ -9,9 +9,9 @@
       type: "line",
       data: {
         datasets: [
-          { label: "CPU %",       data: series.cpu_pct.map(p => ({x: p.t, y: p.v})) },
-          { label: "Mem %",       data: series.mem_used_pct.map(p => ({x: p.t, y: p.v})) },
-          { label: "Disk % worst", data: series.disk_used_pct_worst.map(p => ({x: p.t, y: p.v})) },
+          { label: "CPU %",  data: series.cpu_pct.map(p => ({x: p.t, y: p.v})) },
+          { label: "Mem %",  data: series.mem_used_pct.map(p => ({x: p.t, y: p.v})) },
+          { label: "Disk / %", data: series.disk_root.map(p => ({x: p.t, y: p.v})) },
         ],
       },
       options: {