docs(feature-control): fix flag key prefix fc. → at. across all docs

Real key pattern is at.<domain>.<name> (e.g. at.ios.only, at.promo).
The fc. prefix in the BFF README and API_Mobile_App.md was incorrect.

- API_Mobile_App.md: updated request keys, response raw examples,
  flag table, and Swift usage examples to at. prefix
- API_Mobile_App.md: clarified that app uses raw["at.key"] not
  simplified flags object (FeatureFlagsState.isEnabled reads raw)
- feature-control-bff/README.md: updated DEFAULTS_JSON example,
  request keys, response flags/raw examples, added note about raw usage

feature-control-bff/README.md

@@ -27,11 +27,10 @@ Exemplo de `FEATURE_CONTROL_DEFAULTS_JSON`:
 
 ```json
 {
-  "fc.promo": { "enabled": true, "variant": "on" },
-  "fc.promo-codes": { "enabled": true, "variant": "on" },
-  "fc.android": { "enabled": true, "variant": "on" },
-  "fc.city-aguai": { "enabled": true, "variant": "on" },
-  "fc.ios": { "enabled": true, "variant": "on" }
+  "at.ios.only":     { "enabled": true,  "variant": "on"  },
+  "at.android.only": { "enabled": true,  "variant": "on"  },
+  "at.promo":        { "enabled": true,  "variant": "on"  },
+  "at.city.aguai":   { "enabled": true,  "variant": "on"  }
 }
 ```
 
@@ -40,7 +39,7 @@ Exemplo de `FEATURE_CONTROL_DEFAULTS_JSON`:
 ```json
 {
   "environment": "production",
-  "keys": ["fc.promo", "fc.promo-codes", "fc.android", "fc.city-aguai", "fc.ios"],
+  "keys": ["at.ios.only", "at.android.only", "at.promo", "at.city.aguai"],
   "context": {
     "subjectType": "customer",
     "subjectId": "cust_123",
@@ -48,8 +47,7 @@ Exemplo de `FEATURE_CONTROL_DEFAULTS_JSON`:
     "platform": "ios",
     "appVersion": "2.3.1",
     "attributes": {
-      "city": "Belo Horizonte",
-      "tier": "gold"
+      "city": "Aguaí"
     }
   }
 }
@@ -66,14 +64,19 @@ Se o app enviar `Authorization: Bearer <JWT>`, o BFF tenta extrair `subjectId` d
   "configVersion": 7,
   "evaluatedAt": "2026-04-16T12:00:00.000Z",
   "flags": {
-    "promo": true,
-    "promoCodes": true,
-    "android": true,
-    "cityAguai": true,
-    "ios": true
+    "atiosonly":     true,
+    "atandroidonly": false,
+    "atpromo":       true,
+    "atcityaguai":   true
   },
   "raw": {
-    "fc.promo": {
+    "at.ios.only": {
+      "enabled": true,
+      "variant": "on",
+      "payload": null,
+      "reason": "rollout"
+    },
+    "at.promo": {
       "enabled": true,
       "variant": "on",
       "payload": null,
@@ -83,6 +86,9 @@ Se o app enviar `Authorization: Bearer <JWT>`, o BFF tenta extrair `subjectId` d
 }
 ```
 
+> O app Swift usa o campo **`raw`** indexado pela chave original (ex: `raw["at.promo"]`). O campo `flags` é uma versão simplificada gerada mecanicamente (pontos removidos).
+```
+
 Quando o upstream falha (ex.: `429`, `500`, timeout), o BFF devolve `fallback` com defaults estáticos.
 
 ## Execução local