feat(anki): support Senren scene-switching field grouping

- Add Senren configuration, duplicate merging, and scene-aligned media fields
- Document Senren setup and enforce Kiku/Senren exclusivity

src/types/config.ts

@@ -285,6 +285,11 @@ export interface ResolvedConfig {
       fieldGrouping: 'auto' | 'manual' | 'disabled';
       deleteDuplicateInAuto: boolean;
     };
+    isSenren: {
+      enabled: boolean;
+      fieldGrouping: 'auto' | 'manual' | 'disabled';
+      deleteDuplicateInAuto: boolean;
+    };
     lapisKiku: {
       wordCardKind: WordCardKind;
     };