feat: SQL filtering, Users admin tab, dashboard polish

- Move ticket filtering from in-memory to SQL WHERE clauses
  (queue_id, status, owner use Drizzle eq/isNull; text search uses ilike;
  custom field filters use EXISTS subqueries)
- Add limit param to GET /tickets
- Add POST/PATCH/DELETE /users routes
- Add Users tab to admin page with create/edit/delete
- Smart widget positioning in dashboard (3-column grid fill)
- Show pattern hint below CF inputs in New Ticket dialog

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

web/src/app/dashboards/[id]/page.tsx

@@ -97,7 +97,15 @@ export default function DashboardPage({ params }: { params: Promise<{ id: string
   const handleAddWidget = async () => {
     if (!addViewId || !addTitle.trim()) return;
     setAdding(true);
-    const pos = { x: 0, y: widgets.length, w: 4, h: 2 };
+    // Smart positioning: fill a 3-column grid (4 units each in 12-col grid)
+    const COLS = 3; const W = 4; const H = 2;
+    const occupied = new Set(widgets.map((w) => `${w.position.x},${w.position.y}`));
+    let x = 0; let y = 0;
+    while (occupied.has(`${x},${y}`)) {
+      x += W;
+      if (x >= COLS * W) { x = 0; y += H; }
+    }
+    const pos = { x, y, w: W, h: H };
     const config = addType === "grouped_counts" ? { group_by: addGroupBy } : {};
     const { data, error } = await createWidget(id, {
       view_id: addViewId,