Add metric sub-team intermediate drill-down view

Clicking a metric now shows a sub-team breakdown page with totals per team
(compliant, non-compliant, total, %) instead of jumping directly to a flat
device list. Clicking a sub-team then shows the device list filtered to
that team only.

Navigation flow: Overview → Vertical → Metric (sub-team totals) → Team (devices)

Backend: added optional ?team= query param to the device list endpoint for
filtered queries.

Frontend: added MetricSubTeamView component with metric-level stats bar and
clickable sub-team table. Updated navigation state to include selectedTeam.

Also updated design brief to reflect the new drill-down hierarchy.

docs/vcl-multi-vertical-design-brief.md

@@ -110,8 +110,15 @@ Executive Overview (all verticals aggregated)
         │     │     │     ├── └ INTELDEV:    233 compliant, 11 NC, 244 total — 95.0%
         │     │     │     └── └ STEAM:       123 compliant, 4 NC, 127 total — 97.0%
         │     │     │
-        │     │     ├── ▸ 7.1.1 (Logging & Monitoring) — 72.0% — 149 NC → click metric
-        │     │     │     └── Device list: hostname, IP, type, team, seen_count, resolution_date
+        │     │     ├── Click metric ID → Metric Sub-Team View
+        │     │     │     ├── Stats: total 66,176 | compliant 64,414 | NC 1,762 | 97% | target 80%
+        │     │     │     └── Sub-Team Table:
+        │     │     │           ├── ACCESS-ENG — 8 total — 88.0% → click
+        │     │     │           │     └── Device list (filtered to ACCESS-ENG)
+        │     │     │           ├── ACCESS-OPS — 65,797 total — 97.0% → click
+        │     │     │           │     └── Device list (filtered to ACCESS-OPS)
+        │     │     │           ├── INTELDEV — 244 total — 95.0% → click
+        │     │     │           └── STEAM — 127 total — 97.0% → click
         │     │     └── ...
         │     │
         │     └── Burndown: blockers, with dates, projected clear date
@@ -197,7 +204,7 @@ Some metrics have a team value of `(Other)` in the Summary sheet. This represent
 
 ### Device-Level Drill-Down
 
-Clicking a metric ID navigates to the device list — individual non-compliant hostnames for that vertical + metric combination. This data comes from the detail sheets (not the Summary sheet) and shows:
+Clicking a sub-team row in the metric sub-team view navigates to the device list — individual non-compliant hostnames for that vertical + metric + team combination. The device list is filtered to only show devices belonging to the selected team. This data comes from the detail sheets (not the Summary sheet) and shows:
 
 - Hostname, IP address, device type, team
 - Seen count (how many consecutive uploads this device has been non-compliant)
@@ -205,6 +212,14 @@ Clicking a metric ID navigates to the device list — individual non-compliant h
 - Resolution date (if set)
 - Remediation plan (if documented)
 
+If a metric has no sub-team breakdown (e.g., only an "(Other)" team), a "View All Devices" button is shown instead, which loads the full unfiltered device list for that metric.
+
+The full navigation path is:
+
+```
+Overview → Vertical → Metric (sub-team totals) → Team (device list)
+```
+
 ---
 
 ## Burndown Forecast