Adds the user-facing layer on top of the Rust license commands shipped
in #46.
- `licenseService.ts` thin wrapper around the new Tauri commands
- `useLicense` hook follows the project's useReducer pattern (idle,
loading, ready, validating, error) and exposes `submitKey`,
`refresh`, and `checkEntitlement` for cross-component use
- `LicenseCard` shows the current edition, the expiry date when set,
accepts a license key with inline validation feedback, and links to
the purchase page via `openUrl` from `@tauri-apps/plugin-opener`
- Card is inserted at the top of `SettingsPage` so the edition is the
first thing users see when looking for license-related actions
- i18n: new `license.*` keys in both `fr.json` and `en.json`
- Bilingual CHANGELOG entries
