Phase 0: UTC-Datumsauswertung korrigiert, Portierungsanalyse und -plan

Vorarbeiten fuer die Linux-/NET-10-Portierung (siehe docs/PLAN-Linux-Portierung.md).

DateTime.TryParse ohne DateTimeStyles liefert bei Z-Zeitstempeln Kind=Local und
rechnet in Lokalzeit um. An 13 Stellen in PolymarketProvider und LimitlessProvider
wurden so ISO-Zeitstempel der Plattform-APIs eingelesen, waehrend der Fallback
derselben Zuweisungen (DateTime.UtcNow) korrektes UTC schrieb - die Spalten
enthielten also gemischt verschobene und korrekte Werte. Auf einem Server mit
TZ=UTC haette derselbe Code andere Werte erzeugt als unter Windows.

Neuer Helfer Infrastructure/Helpers/DateParsing.cs kapselt das Parsen mit
InvariantCulture und AdjustToUniversal|AssumeUniversal; alle Fundstellen umgestellt.

Ausserdem:
- LimitlessProvider: Volume-Parsing auf InvariantCulture umgestellt
- EmbeddedWebServer: hartkodierten j:\-Absolutpfad als wwwroot-Fallback entfernt

Ein Backfill der Altdaten erfolgt bewusst nicht.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/Predictalytics.Infrastructure/Helpers/DateParsing.cs

@@ -0,0 +1,34 @@
+using System.Globalization;
+
+namespace Predictalytics.Infrastructure.Helpers;
+
+/// <summary>
+/// Parses timestamp strings from platform APIs as UTC.
+/// <para>
+/// The platforms deliver ISO-8601 strings; the domain stores UTC throughout — every call
+/// site falls back to <see cref="DateTime.UtcNow"/>, and the neighbouring DbCreatedAt is
+/// always UTC. A plain <c>DateTime.TryParse</c> breaks that in two ways: it honours the
+/// machine's locale, and it converts a "Z"-suffixed timestamp to <em>local</em> time. The
+/// same API payload would therefore land in the database differently on a Berlin
+/// workstation than on a UTC server.
+/// </para>
+/// </summary>
+public static class DateParsing
+{
+    private const DateTimeStyles UtcStyles =
+        DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal;
+
+    /// <summary>
+    /// Parses an API timestamp as UTC. Returns null when absent or unparseable.
+    /// Timestamps without a zone designator are treated as UTC.
+    /// </summary>
+    public static DateTime? ParseUtc(string? value) =>
+        DateTime.TryParse(value, CultureInfo.InvariantCulture, UtcStyles, out var parsed)
+            ? parsed
+            : null;
+
+    /// <summary>
+    /// Parses an API timestamp as UTC, falling back to the current UTC time.
+    /// </summary>
+    public static DateTime ParseUtcOrNow(string? value) => ParseUtc(value) ?? DateTime.UtcNow;
+}

src/Predictalytics.Infrastructure/Providers/Limitless/LimitlessProvider.cs

@@ -1,6 +1,8 @@
+using System.Globalization;
 using Predictalytics.Domain.Entities;
 using Predictalytics.Domain.Enums;
 using Predictalytics.Domain.Interfaces;
+using Predictalytics.Infrastructure.Helpers;
 using Predictalytics.Infrastructure.Logging;
 using Microsoft.Extensions.Logging;
 
@@ -235,7 +237,7 @@ public class LimitlessProvider : IPlatformProvider
                     Price = (decimal)(e.Price ?? 0),
                     Size = (decimal)(e.Size ?? 0),
                     Amount = (decimal)(e.Price * e.Size ?? 0),
-                    ExecutedAt = DateTime.TryParse(e.CreatedAt, out var dt) ? dt : DateTime.UtcNow,
+                    ExecutedAt = DateParsing.ParseUtcOrNow(e.CreatedAt),
                     TransactionHash = e.TxHash,
                     TransientWallet = wallet,
                 };
@@ -265,11 +267,12 @@ public class LimitlessProvider : IPlatformProvider
             Category = catMap.Category,
             Subcategory = catMap.Subcategory,
             ImageUrl = raw.ImageUrl ?? "",
-            Volume = decimal.TryParse(raw.VolumeFormatted?.Replace(" USDC", ""), out var vol) ? vol : 0,
+            Volume = decimal.TryParse(raw.VolumeFormatted?.Replace(" USDC", ""),
+                NumberStyles.Any, CultureInfo.InvariantCulture, out var vol) ? vol : 0,
             Liquidity = (decimal)(raw.Liquidity ?? 0),
             EndDate = (raw.ExpirationTimestamp.HasValue && raw.ExpirationTimestamp.Value > 0 && raw.ExpirationTimestamp.Value < 253402300799)
-                ? DateTimeOffset.FromUnixTimeSeconds(raw.ExpirationTimestamp.Value).UtcDateTime 
-                : (DateTime.TryParse(raw.ExpirationDate, out var ed) ? ed : null),
+                ? DateTimeOffset.FromUnixTimeSeconds(raw.ExpirationTimestamp.Value).UtcDateTime
+                : DateParsing.ParseUtc(raw.ExpirationDate),
             IsResolved = raw.Closed,
             LastUpdatedAt = DateTime.UtcNow
         };

src/Predictalytics.Infrastructure/Providers/Polymarket/PolymarketProvider.cs

@@ -2,6 +2,7 @@ using System.Text.Json;
 using Predictalytics.Domain.Entities;
 using Predictalytics.Domain.Enums;
 using Predictalytics.Domain.Interfaces;
+using Predictalytics.Infrastructure.Helpers;
 using Predictalytics.Infrastructure.Logging;
 using Microsoft.Extensions.Logging;
 
@@ -216,9 +217,9 @@ public class PolymarketProvider : IPlatformProvider
                 Title = rawEv.Title,
                 Description = rawEv.Description,
                 ImageUrl = rawEv.Image,
-                StartDate = DateTime.TryParse(rawEv.StartDate, out var esd) ? esd : null,
-                EndDate = DateTime.TryParse(rawEv.EndDate, out var eed) ? eed : null,
-                CreatedAt = DateTime.TryParse(rawEv.CreatedAt, out var ecd) ? ecd : DateTime.UtcNow,
+                StartDate = DateParsing.ParseUtc(rawEv.StartDate),
+                EndDate = DateParsing.ParseUtc(rawEv.EndDate),
+                CreatedAt = DateParsing.ParseUtcOrNow(rawEv.CreatedAt),
                 DbCreatedAt = DateTime.UtcNow,
                 IsActive = rawEv.Active,
                 IsClosed = rawEv.Closed,
@@ -312,9 +313,9 @@ public class PolymarketProvider : IPlatformProvider
             Title = rawEvent.Title,
             Description = rawEvent.Description,
             ImageUrl = rawEvent.Image,
-            StartDate = DateTime.TryParse(rawEvent.StartDate, out var sd) ? sd : null,
-            EndDate = DateTime.TryParse(rawEvent.EndDate, out var ed) ? ed : null,
-            CreatedAt = DateTime.TryParse(rawEvent.CreatedAt, out var cd) ? cd : DateTime.UtcNow,
+            StartDate = DateParsing.ParseUtc(rawEvent.StartDate),
+            EndDate = DateParsing.ParseUtc(rawEvent.EndDate),
+            CreatedAt = DateParsing.ParseUtcOrNow(rawEvent.CreatedAt),
             DbCreatedAt = DateTime.UtcNow,
             IsActive = rawEvent.Active,
             IsClosed = rawEvent.Closed,
@@ -359,14 +360,14 @@ public class PolymarketProvider : IPlatformProvider
             Volume = (decimal)raw.Volume,
             Volume24h = (decimal)raw.Volume24hr,
             Liquidity = (decimal)raw.Liquidity,
-            StartDate = DateTime.TryParse(raw.StartDate, out var msd) ? msd : null,
-            EndDate = DateTime.TryParse(raw.EndDate ?? raw.EndDateIso, out var med) ? med : null,
-            CreatedAt = DateTime.TryParse(raw.CreatedAt, out var mcd) ? mcd : DateTime.UtcNow,
+            StartDate = DateParsing.ParseUtc(raw.StartDate),
+            EndDate = DateParsing.ParseUtc(raw.EndDate ?? raw.EndDateIso),
+            CreatedAt = DateParsing.ParseUtcOrNow(raw.CreatedAt),
             DbCreatedAt = DateTime.UtcNow,
             LastUpdatedAt = DateTime.UtcNow,
             FeeRateBps = (decimal)(raw.TakerFee * 10000),
             IsNegRisk = raw.NegRisk,
-            ClosedAt = DateTime.TryParse(raw.ClosedTime, out var mct) ? mct : null
+            ClosedAt = DateParsing.ParseUtc(raw.ClosedTime)
         };
 
         // Parse outcomes, prices, and token IDs from JSON strings

src/Predictalytics.WinFormsHost/Services/EmbeddedWebServer.cs

@@ -315,9 +315,7 @@ public class EmbeddedWebServer
             Path.Combine(baseDir, "wwwroot"),
             // From bin/Debug/net8.0-windows/ up to src/, then into Api/wwwroot
             Path.GetFullPath(Path.Combine(baseDir, "..", "..", "..", "..", "Predictalytics.Api", "wwwroot")),
-            Path.GetFullPath(Path.Combine(baseDir, "..", "..", "..", "..", "..", "src", "Predictalytics.Api", "wwwroot")),
-            // Absolute fallback for this specific workspace
-            @"j:\Softwareprojekte\Predictalytics\Predictalytics\src\Predictalytics.Api\wwwroot"
+            Path.GetFullPath(Path.Combine(baseDir, "..", "..", "..", "..", "..", "src", "Predictalytics.Api", "wwwroot"))
         };
 
         foreach (var path in candidates)