What
Add a user-configurable default (home) currency. The subscription tracker header should show a single aggregated total converted to that currency, alongside the existing per-currency breakdown.
Why
Users with subscriptions in multiple currencies (e.g. CZK + USD) currently have to mentally sum across currency blocks. A single home-currency total removes that friction.
Acceptance criteria
- User can set a default currency in settings (persisted to SQLite)
- Header shows a converted total in the home currency (e.g. "~CZK 1 200/mo") using a stored or manually-entered exchange rate
- Per-currency breakdown remains visible below the aggregate
- Exchange rates are manually entered by the user (no live API needed for MVP — avoids external dependency and key management)
- Settings accessible from the Subscriptions view or global settings screen
What
Add a user-configurable default (home) currency. The subscription tracker header should show a single aggregated total converted to that currency, alongside the existing per-currency breakdown.
Why
Users with subscriptions in multiple currencies (e.g. CZK + USD) currently have to mentally sum across currency blocks. A single home-currency total removes that friction.
Acceptance criteria