[AZ-370] Refactor C17: status / point-type enums + AC RT2 update

Replaces bare strings with two enums in Common/Enums/:
  RegionStatus { Queued, Processing, Completed, Failed }
  RoutePointType { Start, End, Action, Intermediate }

Adds a Dapper EnumStringTypeHandler<T> (DataAccess/TypeHandlers/)
that round-trips enums to/from lowercase strings, registered once
at startup via DapperEnumTypeHandlers.RegisterAll(). DataAccess now
references Common (project ref) so entities can carry the enum types.

Sites converted: RegionService (5), RouteProcessingService (3),
RoutePointGraphBuilder (4), entity Status/PointType columns. Log
message and summary file format preserved via .ToLowerInvariant().

API JSON contract preserved by adding JsonStringEnumConverter with
JsonNamingPolicy.CamelCase to the http JSON options — single-word
enum members serialize to the same lowercase strings as before.

DTO renamed: Common.DTO.RegionStatus -> RegionStatusResponse to
free the RegionStatus name for the new enum (forced by the task's
explicit enum name); the renamed DTO has no public-API impact at
the JSON wire level. Stale doc references updated.

AC RT2 in _docs/00_problem/acceptance_criteria.md now lists all 4
point types (start/end/action/intermediate).

Tests: 171 / 171 unit + 5 / 5 smoke green (was 141 + 5; +30 new tests
covering type handler round-trip, set/parse, unknown-value rejection,
idempotent registration, and the AC RT2 doc check).

Co-authored-by: Cursor <cursoragent@cursor.com>

SatelliteProvider.DataAccess/TypeHandlers/EnumStringTypeHandler.cs

@@ -0,0 +1,51 @@
+using System.Data;
+using Dapper;
+using SatelliteProvider.Common.Enums;
+
+namespace SatelliteProvider.DataAccess.TypeHandlers;
+
+public class EnumStringTypeHandler<T> : SqlMapper.TypeHandler<T> where T : struct, Enum
+{
+    public override T Parse(object value)
+    {
+        if (value is null || value is DBNull)
+        {
+            throw new DataException($"Cannot parse null DB value into enum {typeof(T).Name}");
+        }
+
+        var s = value as string ?? value.ToString();
+        if (string.IsNullOrEmpty(s))
+        {
+            throw new DataException($"Cannot parse empty DB value into enum {typeof(T).Name}");
+        }
+
+        if (!Enum.TryParse<T>(s, ignoreCase: true, out var parsed) || !Enum.IsDefined(parsed))
+        {
+            throw new DataException($"DB value '{s}' is not a defined member of enum {typeof(T).Name}");
+        }
+
+        return parsed;
+    }
+
+    public override void SetValue(IDbDataParameter parameter, T value)
+    {
+        parameter.Value = value.ToString().ToLowerInvariant();
+        parameter.DbType = DbType.String;
+    }
+}
+
+public static class DapperEnumTypeHandlers
+{
+    private static int _registered;
+
+    public static void RegisterAll()
+    {
+        if (Interlocked.Exchange(ref _registered, 1) == 1)
+        {
+            return;
+        }
+
+        SqlMapper.AddTypeHandler(new EnumStringTypeHandler<RegionStatus>());
+        SqlMapper.AddTypeHandler(new EnumStringTypeHandler<RoutePointType>());
+    }
+}