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>

frontend/src/hooks/useApi.ts

@@ -20,6 +20,34 @@ export type TickerValidation = { valid: boolean; symbol: string; name?: string;
 export const validateTicker = (symbol: string): Promise<TickerValidation> =>
   api.get('/market/validate', { params: { symbol } }).then(r => r.data)
 
+export const useMarketCustomTickers = () =>
+  useQuery<{ ticker: string; name: string; added_at: string }[]>({
+    queryKey: ['market-custom-tickers'],
+    queryFn: () => api.get('/market/custom-tickers').then(r => r.data),
+  })
+
+export const useAddMarketTicker = () => {
+  const qc = useQueryClient()
+  return useMutation({
+    mutationFn: (ticker: string) => api.post(`/market/custom-tickers/${encodeURIComponent(ticker)}`).then(r => r.data),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['market-custom-tickers'] })
+      qc.invalidateQueries({ queryKey: ['quotes'] })
+    },
+  })
+}
+
+export const useRemoveMarketTicker = () => {
+  const qc = useQueryClient()
+  return useMutation({
+    mutationFn: (ticker: string) => api.delete(`/market/custom-tickers/${encodeURIComponent(ticker)}`).then(r => r.data),
+    onSuccess: () => {
+      qc.invalidateQueries({ queryKey: ['market-custom-tickers'] })
+      qc.invalidateQueries({ queryKey: ['quotes'] })
+    },
+  })
+}
+
 export const useHistory = (symbol: string, period = '1y', interval = '1d') =>
   useQuery<HistoricalCandle[]>({
     queryKey: ['history', symbol, period, interval],