ux: inconsistent amount flag naming across commands

## Description

Different command groups use different flag names for AVAX amounts:
- Transfer commands: `--amount` / `--amount-navax`
- Validator commands: `--stake`
- L1 commands: `--balance`

## Impact

Users must remember different flag names for the same concept (an AVAX amount) depending on the command.

## Suggestion

Consider adding precision alternatives consistently:
- `--stake-navax` for validator commands
- `--balance-navax` for L1 commands

Or document the rationale for semantic naming in help text.

## Files affected
- `cmd/transfer.go` - uses `--amount` / `--amount-navax`
- `cmd/validator.go` - uses `--stake`
- `cmd/l1.go` - uses `--balance`

## Severity
Medium UX impact

## Source
CLI UX audit (2026-02-09)