feat: dynamic market ticker watchlist (Markets page)

Add ability to add/remove custom tickers (e.g. EURCHF=X) on the
Markets & Prices page without editing config. Tickers are validated
via yfinance, persisted in market_watchlist SQLite table, merged into
the quotes feed as a 'custom' group, and shown in a dedicated tab
with per-card remove buttons.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/data_fetcher.py

@@ -136,6 +136,24 @@ def get_all_quotes() -> Dict[str, List[Dict[str, Any]]]:
                 q["asset_class"] = asset_class
                 quotes.append(q)
         result[asset_class] = quotes
+
+    # User-added custom tickers
+    try:
+        from services.database import get_market_custom_tickers
+        custom_entries = get_market_custom_tickers()
+        if custom_entries:
+            custom_quotes = []
+            for entry in custom_entries:
+                q = get_quote(entry["ticker"])
+                if q:
+                    q["name"] = entry["name"] or entry["ticker"]
+                    q["asset_class"] = "custom"
+                    custom_quotes.append(q)
+            if custom_quotes:
+                result["custom"] = custom_quotes
+    except Exception:
+        pass
+
     return result