Add more currency options (AUD, CAD, JPY, CHF)

[Rishiidev]

Submap currently supports USD, EUR, INR, and GBP. Many users want to track in other currencies.

What to add:
Support for at least these currencies in src/types.ts:

Code	Symbol	Label
AUD	A$	Australian Dollar
CAD	C$	Canadian Dollar
JPY	¥	Japanese Yen
CHF	Fr	Swiss Franc

How to do it:

1. Open src/types.ts
2. Add entries to the CurrencyCode type and the CURRENCIES array:

export type CurrencyCode = 'USD' | 'EUR' | 'INR' | 'GBP' | 'AUD' | 'CAD' | 'JPY' | 'CHF';

3. Add each currency object to CURRENCIES:

{ code: 'AUD', symbol: 'A$', label: 'Australian Dollar' },

4. Run npm run lint — no TypeScript errors should appear
5. Test: open the app, go to Settings, confirm the new currencies appear in the selector

Why this helps: Submap already has locale-correct formatting, so new currencies just work once added to the type definition. No backend changes needed.

No deep knowledge required — this is a great first contribution.