feat(converter): add shareable conversion links via query parameters

README.md

@@ -15,6 +15,7 @@ Modern currency and crypto converter built with Next.js 14, TypeScript, Tailwind
   - Fiat flags from `currency-flags`
 - Default pair: `USD -> BTC`
 - Instant conversion with swap action
+- Shareable conversion links via query params (`amount`, `from`, `to`)
 - Current rate, inverse rate, and last update timestamp
 - Client-side validation for invalid/negative amounts
 - Loading, error, and empty states
@@ -166,6 +167,22 @@ If empty, the app uses the local default (`/api/rates`).
   - Supported ranges: `24h`, `7d`, `30d`, `1y`, `all`.
   - Example response fields: `priceUsd`, `change24hPct`, `marketCapUsd`, `volume24hUsd`, `priceHistoryRange`, `priceHistory`, `updatedAt`.
 
+## Shareable Links
+
+You can share the current converter state using URL query params:
+
+- `amount`
+- `from`
+- `to`
+
+Example:
+
+```text
+/?amount=100&from=USD&to=BTC
+```
+
+The app safely parses these params on load and falls back to defaults when values are invalid or unsupported.
+
 ## Architecture Notes
 
 - `app/api/rates/route.ts` is the single internal market endpoint for the frontend.