feat(portfolio): store and publish instrument sector and issuer (WealthLedger/main#48)

prisma/schema.prisma

@@ -186,6 +186,20 @@ model TbankInstrumentLookup {
   @@id([provider, identifierType, identifier])
 }
 
+// Public per-instrument classification; no holdings or credentials.
+model TbankInstrumentClassification {
+  provider        String
+  instrumentKey   String
+  sector          String?
+  sectorFetchedAt DateTime?
+  assetUid        String?
+  brandUid        String?
+  brandName       String?
+  brandFetchedAt  DateTime?
+
+  @@id([provider, instrumentKey])
+}
+
 // Source records contain no holdings, personal estimates or credentials errors.
 model TbankInstrumentSource {
   provider String