Add ZIP-wrapped CAMT parsing and real bank file tests

- Support parsing camt.052 ZIP archives in CamtParser and BankingService
- Add CamtZipParserTests for ZIP parsing (single/multi/malformed/empty cases)
- Add CamtRealFileTests: integration tests for real bank exports (ZIP, XML, CAMT, MT940, STA) in git-ignored test data dir
- Update .gitignore and add README.md for test data usage
- Copy test data files in Fuchs.Tests.csproj; add .gitkeep
- Refactor BankingService CAMT mapping logic
- Overhaul connection string config: use {username}/{password} tokens, resolve from secrets at runtime, update appsettings and Key Vault keys

Fuchs/appsettings.Development.json

@@ -1,4 +1,8 @@
-{
+{
+  "ConnectionStrings": {
+    "ocms_ConnectionString": "Server=localhost;Database=ocms;User Id=DEV_USERNAME;Password=DEV_PASSWORD;TrustServerCertificate=True;",
+    "fuchs_fds_ConnectionString": "Server=localhost;Database=fuchs_fds;User Id=DEV_USERNAME;Password=DEV_PASSWORD;TrustServerCertificate=True;"
+  },
   "Logging": {
     "LogLevel": {
       "Default": "Debug",