config: update import column mapping to match ODS structure

Rename app.import.excel.col.* → app.import.col.* and set correct
column indices for all fields in the ODS spreadsheet.

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

backend/src/main/resources/application.yaml

@@ -40,9 +40,14 @@ app:
     password: ${APP_ADMIN_PASSWORD:admin123}
 
   import:
-    excel:
-      col:
-        filename: 0
-        date: 1
-        location: 2
-        transcription: 3
+    col:
+      index: 0
+      box: 1
+      folder: 2
+      sender: 3
+      receivers: 5
+      date: 7
+      location: 9
+      tags: 10
+      summary: 11
+      transcription: 13