Dashboard grid: 1-col min width for stats, vertical compaction for make-room dragging

- Stat widgets can now be resized down to a single column (minW 1)
- Switch to vertical compaction so dragging a widget pushes others down to reveal the drop spot, then settles (fixes both the no-move and fly-off behaviours)

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

frontend/src/pages/DashboardPage.jsx

@@ -45,7 +45,7 @@ const STAT_DEFS = {
 
 // Full widget registry: size defaults + palette label. Stats inherit from STAT_DEFS.
 const WIDGETS = {
-  ...Object.fromEntries(Object.entries(STAT_DEFS).map(([id, d]) => [id, { label: d.label, w: 2, h: 1, minW: 2, minH: 1 }])),
+  ...Object.fromEntries(Object.entries(STAT_DEFS).map(([id, d]) => [id, { label: d.label, w: 2, h: 1, minW: 1, minH: 1 }])),
   weekly:      { label: 'Weekly distance',  w: 6, h: 3, minW: 4, minH: 2 },
   bodyBattery: { label: 'Body Battery',     w: 4, h: 3, minW: 3, minH: 2 },
   vo2maxTrend: { label: 'VO₂ max trend',    w: 3, h: 3, minW: 2, minH: 2 },
@@ -629,8 +629,7 @@ export default function DashboardPage() {
         isDraggable={editMode}
         isResizable={editMode}
         onLayoutChange={handleLayoutChange}
-        compactType={null}
-        preventCollision
+        compactType="vertical"
         draggableCancel=".widget-delete"
       >
         {layout.filter(l => WIDGETS[l.i]).map(l => (