chore(ui): align TrendCard heading weight, account form rhythm, and MoodChart tick margin with siblings

Three single-class polish swaps to retire P0 / P1 drifts the UI-
conformity review caught:

- TrendCard headline number was the only dashboard tile using
  font-bold for its hero value; every sibling renders the same
  numeric role at font-semibold. Align so the trend strip reads
  uniformly.
- account-section password form was the only form in the codebase
  on space-y-3 outer rhythm; every other form uses space-y-4. Lift
  to match.
- mood-chart YAxis tickMargin sat at 6 while every other line chart
  passes 10 from the same canonical recipe. Match so mood labels
  sit at the same distance from the axis as siblings.

src/components/settings/account-section.tsx

@@ -610,7 +610,7 @@ export function AccountSection() {
             </DialogDescription>
           </DialogHeader>
 
-          <form onSubmit={handleChangePassword} className="space-y-3">
+          <form onSubmit={handleChangePassword} className="space-y-4">
             <div className="grid gap-3 sm:grid-cols-3">
               <div className="space-y-2">
                 <Label htmlFor="current-password">