Fix trading sheet tab bar spacing

[dannyhw]

Summary

Fixes spacing for the trading flow around the native bottom tab bar.

The trade bottom sheet now receives the tab bar inset from the asset details screen and uses it as bottom content padding, so the sheet content stays clear of the tabs while the sheet can still present from the bottom. The trade button footer also keeps compact Android padding while preserving iOS tab bar clearance.

The iOS tab bar height can briefly report as zero on initial render, so the details screen uses a standard tab bar height plus safe-area inset as a fallback.

Test plan

• Open an asset details screen on iOS and tap Trade. Confirm the bottom sheet actions are not covered by the tab bar.
• Focus the amount input on iOS. Confirm the sheet works with the keyboard open and with keyboard closed
• Open an asset details screen on Android. Confirm the sheet works with the keyboard open and with keyboard closed