Add Romanian Leu (RON) currency to menubar and GNOME extension

[ozymandiashh]

What

Adds Romanian Leu (RON) to the currency picker in the macOS menubar app and GNOME extension.

Why

The CLI already supports any ISO 4217 currency code dynamically via Intl.NumberFormat + Frankfurter API (162 currencies). However, the macOS menubar app uses a fixed SupportedCurrency enum, and the GNOME extension uses a hardcoded CURRENCIES array. RON was missing from both, so users on these surfaces could not select Romanian Leu despite it being a valid ISO 4217 code.

Changes

File	Change
mac/Sources/CodeBurnMenubar/AppStore.swift	Added RON case to SupportedCurrency enum + "Romanian Leu" displayName
mac/Sources/CodeBurnMenubar/CurrencyState.swift	Added "RON": "lei" to symbolOverrides
gnome/indicator.js	Added { code: "RON", symbol: "lei " } to CURRENCIES array

Notes

• Symbol uses lei (the common Romanian shorthand) rather than the ISO code RON, consistent with how SEK/DKK use kr instead of the ISO code.
• Exchange rates are already fetched from Frankfurter (ECB data) which supports RON.
• No CLI changes needed — src/currency.ts validates dynamically via Intl.NumberFormat.
• No test changes needed — currency validation in CLI is dynamic, and the menubar/GNOME currency lists are not covered by automated tests.

Testing

• TypeScript test suite: 1387 passed, 8 failed (all pre-existing failures on main, unrelated to this change — confirmed by running tests on clean main).
• Verified RON is a valid ISO 4217 code and is supported by the Frankfurter API.
• Swift changes are straightforward enum additions following the exact pattern of existing cases.