Binance UX: fiat precision, lot size info & network error handling

[nehasvit]

Summary

• Fiat display precision: amounts now show 2 decimal places (e.g. 4.36 instead of 4), with a separate fiatWhole() formatter for chart axes
• Binance LOT_SIZE info: parameterized note per crypto (BTC, ETH, BNB, SOL, ADA, DOT) shown in plan form (Add/Edit/FirstPlan) and as an info dialog in Plan Details
• Network error handling: new NetworkError sealed variant in credential validation with localized message (error_no_internet) in both EN and CS

Changed files (16)

• NumberFormatters.kt — fiat() → 2 decimals, new fiatWhole() for charts
• Models.kt — Exchange.binanceLotStepSize map with real Binance step sizes
• ValidateAndSaveCredentialsUseCase.kt — NetworkError sealed variant
• CredentialFormDelegate.kt — @StringRes error support, resolvedCredentialsError composable extension
• PlanFormContent.kt — lot size info row for Binance
• PlanDetailsScreen.kt — info icon + AlertDialog for lot size
• EditPlanViewModel.kt / EditPlanScreen.kt — pass exchange to form
• AddPlanScreen.kt / FirstPlanScreen.kt — pass exchange to form
• AddPlanViewModel.kt — handle NetworkError
• AddExchangeScreen.kt / ExchangeDetailScreen.kt / ExchangeSetupScreen.kt — use resolvedCredentialsError
• strings.xml (EN + CS) — binance_lot_size_note, error_no_internet

Test plan

• Verify fiat amounts display with 2 decimal places in plan details and dashboard
• Verify chart Y-axis labels still show whole numbers
• Create/edit a Binance plan → lot size note appears under amount for each crypto
• View Binance plan details → info icon next to amount, tap opens dialog with correct crypto/step size
• Non-Binance plans show no lot size info
• Disconnect network → try adding exchange credentials → localized "no internet" error in both EN and CS
• Release build: confirm strings render correctly (no R8 issues)

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