dashboard: PCs not reporting, and the card styling standard it broke

Second wave-one card. GET /api/computers/dashboard/quiet lists two populations
and deliberately does not merge them into one count. A PC that reported and
went quiet is probably off, moved or broken. A PC that has NEVER reported is
worse: not enrolled, or enrolled against the wrong pc-type, so nothing enforces
anything on it and no backup of it exists. That one hides indefinitely because
nothing about it fails loudly - the same shape as the bay that carried a wrong
machine number for weeks.

Never-reported sorts above the merely quiet, then longest silence first: the
order someone should work down the list, not the order rows left the table. A
soft-deleted PC is excluded - a decommissioned machine is silent on purpose,
and listing it would train people to ignore the card, which is the failure this
whole board exists to avoid.

The window is computers_quietreporthours, default 24, because every site will
disagree with any number picked here (ADR-015). A malformed value falls back
rather than failing the card.

This also replaces the computers plugin's old widget declaration, which named a
component nobody ever wrote. Four such declarations remain and will convert as
their cards arrive.

Two fixes to the renderer found while wiring this up. Meta specs now support a
trailing unit, so a row reads 'quiet for 3 days' rather than 'quiet for 3'. And
the card styles hardcoded hex colours against the frontend standard, including
a var(--card-bg) that DOES NOT EXIST - the variable is --bg-card - so the
fallback would have painted every card white and broken dark mode entirely.
Now --bg-card, --border, --danger, --warning, --primary and --link throughout.

plugins/computers/api/routes.py

@@ -934,3 +934,63 @@ def dashboard_summary():
         'shopfloor': shopfloor_count,
         'nonshopfloor': total - shopfloor_count
     })
+
+
+@computers_bp.route('/dashboard/quiet', methods=['GET'])
+@jwt_required()
+@require_permission('computers.view')
+def dashboard_quiet():
+    """PCs that have stopped reporting, and PCs that never started.
+
+    Two populations, deliberately distinguished rather than merged into one
+    count. A PC that reported and went quiet is probably switched off, moved or
+    broken. A PC that has NEVER reported is worse: it is either not enrolled, or
+    enrolled against the wrong pc-type, so nothing enforces anything on it and
+    no backup of it exists. That one hides indefinitely because nothing about it
+    is failing loudly - and it is exactly the shape of the bay that carried a
+    wrong machine number for weeks.
+
+    Silence is the only signal available here. There is no heartbeat separate
+    from the report, so 'stopped reporting' is measured against the collector's
+    own last write.
+    """
+    from datetime import datetime, timedelta, timezone
+
+    hours = 24
+    setting = Setting.query.filter_by(key='computers_quietreporthours').first()
+    if setting and (setting.value or '').strip():
+        try:
+            hours = int(setting.value)
+        except (TypeError, ValueError):
+            pass
+    cutoff = datetime.now(timezone.utc).replace(tzinfo=None) - timedelta(hours=hours)
+
+    query = (db.session.query(Computer, Asset)
+             .join(Asset, Asset.assetid == Computer.assetid)
+             .filter(Asset.isactive.is_(True)))
+
+    rows = []
+    for comp, asset in query.all():
+        last = comp.lastreporteddate
+        if last is None:
+            rows.append({
+                'computerid': comp.computerid,
+                'hostname': comp.hostname,
+                'state': 'never reported',
+                'lastreported': None,
+                'quietdays': None,
+            })
+        elif last < cutoff:
+            rows.append({
+                'computerid': comp.computerid,
+                'hostname': comp.hostname,
+                'state': 'stopped reporting',
+                'lastreported': last.isoformat() + 'Z',
+                'quietdays': (datetime.now(timezone.utc).replace(tzinfo=None)
+                              - last).days,
+            })
+
+    # Never-reported first, then longest silence: the order someone should work
+    # down the list, not the order the rows came out of the table.
+    rows.sort(key=lambda r: (r['quietdays'] is not None, -(r['quietdays'] or 0)))
+    return success_response(rows[:50])