fix(ui): show correct duration for fee rate

[pwltr]

Description

• show correct duration for fee rate where applicable (transaction speed settings, send fee rate, boost sheet)
• Route fee estimation usage through FeeEstimatesManager; remove direct blocktank.fees() calls
• Activity: design updates v59 (activity icons, text)
• force .modern, .bitcoin denomination for custom fee UI
• add "override fees" dev setting to be able to debug fee estimation UI
• update localization keys and strings
• ActivityListViewModel/TransferViewModel: drop unnecesary fee estimation refresh (payOrder takes required satsPerVbyte, estimates cache warmed in ActivityList/ActivityLatest .task)

Screenshot / Video

[pwltr]

Drafted to give precedence to other PRs