fix(currency): resolve RON symbol to "lei" across all surfaces

RON was added to the native macOS/GNOME pickers but not to the shared
SYMBOL_OVERRIDES map, so the CLI, CSV/JSON export, and web dashboard
resolved it through Intl to "RON" while native UI showed "lei" — a
cross-surface split for GNOME/CLI-set currency. Mirror the CNY precedent
(906c533): symbol override + fraction-digits test + README example.

README.md

@@ -410,6 +410,7 @@ codeburn currency GBP          # set to British Pounds
 codeburn currency AUD          # set to Australian Dollars
 codeburn currency JPY          # set to Japanese Yen
 codeburn currency CNY          # set to Chinese Yuan
+codeburn currency RON          # set to Romanian Leu
 codeburn currency              # show current setting
 codeburn currency --reset      # back to USD
 ```

src/currency.ts

@@ -30,6 +30,7 @@ let active: CurrencyState = { code: 'USD', rate: 1, symbol: '$' }
 const USD: CurrencyState = { code: 'USD', rate: 1, symbol: '$' }
 const SYMBOL_OVERRIDES: Record<string, string> = {
   CNY: '¥',
+  RON: 'lei',
 }
 
 // Intl.NumberFormat throws on invalid ISO 4217 codes, so we use it as a validator

tests/currency-rounding.test.ts

@@ -101,5 +101,6 @@ describe('getFractionDigits', () => {
     expect(getFractionDigits('GBP')).toBe(2)
     expect(getFractionDigits('INR')).toBe(2)
     expect(getFractionDigits('CNY')).toBe(2)
+    expect(getFractionDigits('RON')).toBe(2)
   })
 })