Add multi-country ITAD deals, configurable currency, and per-source filtering

- ITAD deals can now be fetched from multiple countries simultaneously via
  ITAD_COUNTRIES (e.g. US,CA,GB,DE). Deals are merged across regions and
  deduplicated by game+shop, with the first country taking priority.

- Prices from non-USD regions are normalised to USD using exchange rates
  so filtering (max price) works consistently across countries.

- ITAD results are now sorted by newest deals first (client-side by
  timestamp) instead of only by highest discount, reducing missed deals.

- Default fetch limit raised from 20 to 100 to capture more deals.

- Display currency is now configurable: DEFAULT_CURRENCY sets the primary
  currency shown first, EXTRA_CURRENCIES sets additional ones. All
  Frankfurter-supported currencies are available with proper symbols.

- Filtering is now per-source with dedicated env vars:
  CHEAPSHARK_MIN_DISCOUNT, CHEAPSHARK_MIN_RATING, CHEAPSHARK_MAX_PRICE,
  ITAD_MIN_DISCOUNT, ITAD_MAX_PRICE, ITAD_DEALS_LIMIT. Shared fallbacks
  (MIN_DISCOUNT_PERCENT, MAX_PRICE) are still supported. Legacy
  MAX_PRICE_USD and MIN_DEAL_RATING continue to work as fallbacks.

https://claude.ai/code/session_01EfPjktyrF24DBNHWsY1KBP

.env.example

@@ -11,10 +11,31 @@ ITAD_API_KEY=
 # Requires ITAD_API_KEY when "itad" is included
 DEAL_SOURCES=cheapshark
 
-# Deal filtering
-MIN_DEAL_RATING=8.0
+# ITAD countries: comma-separated ISO 3166-1 alpha-2 country codes
+# Deals are fetched for each country and merged (duplicates removed).
+# Examples: US, CA, GB, DE, FR, AU, BR, JP
+ITAD_COUNTRIES=US
+
+# Currency display
+# DEFAULT_CURRENCY is shown first; EXTRA_CURRENCIES are shown after it.
+DEFAULT_CURRENCY=USD
+EXTRA_CURRENCIES=CAD,EUR,GBP
+
+# CheapShark-specific filtering
+# (Falls back to shared MIN_DISCOUNT_PERCENT / MAX_PRICE if not set)
+#CHEAPSHARK_MIN_DISCOUNT=50
+#CHEAPSHARK_MIN_RATING=8.0
+#CHEAPSHARK_MAX_PRICE=20
+
+# ITAD-specific filtering
+# (Falls back to shared MIN_DISCOUNT_PERCENT / MAX_PRICE if not set)
+#ITAD_MIN_DISCOUNT=50
+#ITAD_MAX_PRICE=20
+#ITAD_DEALS_LIMIT=100
+
+# Shared filter defaults (used when source-specific values are not set)
 MIN_DISCOUNT_PERCENT=50
-MAX_PRICE_USD=20
+MAX_PRICE=20
 
 # Send an intro message to the room on startup (true/false)
 SEND_INTRO_MESSAGE=false