Add per-firm banned symbols feature

- lib/db.ts: new firm_banned_symbols table with getBannedSymbols,
  isSymbolBanned, and setBannedSymbol helpers
- app/api/firms/[id]/banned-symbols/route.ts: GET lists banned symbols,
  PATCH toggles a ban for a given symbol
- app/api/firms/route.ts: include bannedSymbols[] in firm list response
- app/firms/[id]/settings/page.tsx: Instruments section shows all
  globally-enabled symbols with a red toggle to ban/unban; banned
  symbols display a "SYMBOL BANNED" pill next to their name
- app/page.tsx: FirmRows shows "ES BANNED" (or current symbol) pill next
  to the firm name when the selected trade symbol is banned for that firm
- lib/auto-trade.ts: skip firms entirely when the trade symbol is banned
- types.ts: add bannedSymbols field to FirmConfig

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

app/page.tsx

@@ -161,7 +161,7 @@ function AccountRow({ account, firm, hideDead, privacy }: { account: AccountStat
     );
 }
 
-function FirmRows({ state, firm, deleteMode, selected, onToggle, hideDead, privacy, sortKey, sortDir }: {
+function FirmRows({ state, firm, deleteMode, selected, onToggle, hideDead, privacy, sortKey, sortDir, tradeSymbol }: {
     state: FirmState;
     firm: FirmConfig;
     deleteMode: boolean;
@@ -171,6 +171,7 @@ function FirmRows({ state, firm, deleteMode, selected, onToggle, hideDead, priva
     privacy: boolean;
     sortKey: SortKey | null;
     sortDir: SortDir;
+    tradeSymbol: string;
 }) {
     const [open, setOpen] = useState(true);
 
@@ -209,6 +210,11 @@ function FirmRows({ state, firm, deleteMode, selected, onToggle, hideDead, priva
                             />
                         )}
                         <span className="font-bold text-sm text-slate-800">{state.firm}</span>
+                        {firm.bannedSymbols?.includes(tradeSymbol) && (
+                            <span className="text-xs bg-red-100 text-red-700 px-1.5 py-0.5 rounded font-semibold">
+                                {tradeSymbol} BANNED
+                            </span>
+                        )}
                     </div>
                 </td>
                 <td /><td /><td /><td />
@@ -540,6 +546,7 @@ export default function Home() {
                                             privacy={privacy}
                                             sortKey={sortKey}
                                             sortDir={sortDir}
+                                            tradeSymbol={tradeSymbol}
                                         />
                                     );
                                 })