Exclude Closed tickets from the dashboard status breakdown chart (#110)

StatsModel::getAllStats()'s by_status breakdown grouped every status
including Closed, unlike by_priority and by_category which already
filter status != 'Closed'. Closed tickets accumulate indefinitely, so
over time the status donut chart's Closed slice comes to dominate it,
squeezing Open/Pending/In Progress down to barely-visible slivers —
exactly the breakdown the chart exists to show at a glance.

Filtered by_status the same way the other two breakdowns already are.
The separate open_tickets/closed_tickets KPI counts are unaffected (a
different query); Closed just no longer appears as a chart segment.

Note: this issue was labeled 'invalid' with no explanation in the body
or comments — checked and it's Gitea's generic stock label (description
"Something is wrong"), not a documented decision that the request itself
was wrong. The described problem is real and reproducible in the code,
so implementing it as filed.

Verified against real MariaDB: seeded 3 open-ish tickets (Open, Pending,
In Progress) and 3 Closed. by_status now returns only the 3 active
statuses; open_tickets/closed_tickets KPI counts are unchanged at 3/3.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0117oBw2jN4kALYeS8HPq4zV

models/StatsModel.php

@@ -148,7 +148,7 @@ class StatsModel
             FROM tickets t WHERE status != 'Closed' AND ($visSQL) GROUP BY priority
             UNION ALL
             SELECT 'status' as type, status as label, COUNT(*) as count
-            FROM tickets t WHERE ($visSQL) GROUP BY status
+            FROM tickets t WHERE status != 'Closed' AND ($visSQL) GROUP BY status
             UNION ALL
             SELECT 'category' as type, category as label, COUNT(*) as count
             FROM tickets t WHERE status != 'Closed' AND ($visSQL) GROUP BY category";