fix(ui): move hide-balance icon into balance cards

[CharlVS]

Summary

• Relocated the hide-balance eye icon from a dedicated row above the statistic cards into the balance cards themselves, saving ~48px of vertical space on both mobile and desktop
• Desktop: icon is now inline with the "Your Balance" caption in the first StatisticCard
• Mobile: icon is positioned in the top-right corner of the BalanceSummaryWidget card

Test plan

• Verify the eye icon appears inline with "Your Balance" caption on desktop
• Verify the eye icon appears in the top-right corner of the balance card on mobile
• Confirm tapping the icon toggles balance visibility across all screens
• Confirm the old dedicated row is gone and vertical space is reclaimed
• Check icon doesn't overlap text on narrow screens or with long locale strings

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