The popup UI had no navigation stack — all back buttons were hardcoded
to specific destinations. This meant navigating Main → Address →
Transaction → Settings → Back would go to Main instead of Transaction.
Changes:
- Add viewStack array to persisted state (survives popup close/reopen)
- Add pushCurrentView(), goBack(), clearViewStack() helpers in helpers.js
- goBack() pops the stack and shows the previous view; falls back to
Main if the stack is empty; re-renders the wallet list when returning
to the Main view
- All ctx.show*() wrappers in index.js now push the current view before
navigating forward
- All back buttons across every view now use goBack() instead of
hardcoded destinations
- Direct showView() calls for forward navigation (Send, Export Private
Key) push before switching
- Stack is cleared on reset-to-root actions: adding a wallet, deleting
the last wallet
- After wallet deletion with remaining wallets, stack is reset to
[main] and settings is re-shown
- After transaction completion (Done button), stack is reset to the
appropriate address context
Closes#134
