Refactor Api-Client

Add Exceptionhandler, AlertService JSON-Converter
AppSettings via DI

Reformat Code

Jugenddienst Stunden/Models/JsonFlexibleIntConverters.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Jugenddienst_Stunden.Models;
+
+internal sealed class JsonFlexibleInt32Converter : JsonConverter<int> {
+    public override int Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) {
+        switch (reader.TokenType) {
+            case JsonTokenType.Number:
+                if (reader.TryGetInt32(out var n)) return n;
+                // Fallback via double to cover edge cases
+                var d = reader.GetDouble();
+                return (int)d;
+            case JsonTokenType.String:
+                var s = reader.GetString();
+                if (string.IsNullOrWhiteSpace(s)) return 0;
+                s = s.Trim();
+                // Some APIs embed id like "141|..." -> take leading numeric part
+                int i = 0;
+                int sign = 1;
+                int idx = 0;
+                if (s.StartsWith("-")) { sign = -1; idx = 1; }
+                for (; idx < s.Length; idx++) {
+                    char c = s[idx];
+                    if (c < '0' || c > '9') break;
+                    i = i * 10 + (c - '0');
+                }
+                if (idx > 0 && (idx > 1 || sign == 1)) return i * sign;
+                if (int.TryParse(s, out var parsed)) return parsed;
+                if (long.TryParse(s, out var l)) return (int)l;
+                throw new JsonException($"Cannot convert string '{s}' to Int32.");
+            case JsonTokenType.Null:
+                return 0;
+            default:
+                throw new JsonException($"Token {reader.TokenType} is not valid for Int32.");
+        }
+    }
+
+    public override void Write(Utf8JsonWriter writer, int value, JsonSerializerOptions options)
+        => writer.WriteNumberValue(value);
+}
+
+internal sealed class JsonFlexibleNullableInt32Converter : JsonConverter<int?> {
+    public override int? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) {
+        if (reader.TokenType == JsonTokenType.Null) return null;
+        // Reuse non-nullable converter
+        var conv = new JsonFlexibleInt32Converter();
+        return conv.Read(ref reader, typeof(int), options);
+    }
+
+    public override void Write(Utf8JsonWriter writer, int? value, JsonSerializerOptions options) {
+        if (value.HasValue) writer.WriteNumberValue(value.Value);
+        else writer.WriteNullValue();
+    }
+}