Reduce exchange rate refresh to twice daily

Be respectful of the free Frankfurter API — ECB rates only update once
a day anyway, so a 12-hour cache TTL is more than sufficient.

https://claude.ai/code/session_01LPpSZFfyh6vdV5HGFWjoQX

README.md

@@ -49,4 +49,4 @@ All configuration is via environment variables (see `.env.example`):
 - **Deduplication**: deals are tracked by game ID + timestamp; duplicates are never reposted
 - **Pruning**: deals older than 30 days are pruned from the database so they can be reposted if they return
 - **One message per deal**: each deal is posted individually so messages are independently linkable and dismissible
-- **Multi-currency pricing**: deal prices are shown in USD, CAD, EUR, and GBP using live exchange rates from the [Frankfurter API](https://api.frankfurter.dev) (ECB data, no API key required). Rates are cached and refreshed hourly.
+- **Multi-currency pricing**: deal prices are shown in USD, CAD, EUR, and GBP using live exchange rates from the [Frankfurter API](https://api.frankfurter.dev) (ECB data, no API key required). Rates are cached and refreshed twice daily.

gaming_deals_bot/currency.py

@@ -1,6 +1,6 @@
 """Currency conversion using the Frankfurter API (ECB rates, no API key required).
 
-Rates are cached in memory and refreshed at most once per hour.
+Rates are cached in memory and refreshed at most twice per day.
 """
 
 import logging
@@ -12,7 +12,7 @@ logger = logging.getLogger(__name__)
 
 FRANKFURTER_URL = "https://api.frankfurter.dev/v1/latest"
 TARGET_CURRENCIES = ("CAD", "EUR", "GBP")
-CACHE_TTL_SECONDS = 3600  # 1 hour
+CACHE_TTL_SECONDS = 43200  # 12 hours — be nice to the free service
 
 # Module-level cache
 _rates: dict[str, float] = {}