fix: make locale-independence real, not assumed — parsing, casing, comparison

Follow-up to the retail-text fix. "Green under sv-SE" is not the same as "runs
on any locale", so this establishes the latter by running the suite under
cultures chosen to break different things, and fixing what they broke.

ar-SA found a genuine defect the Swedish runner cannot see: the resolution
parser read "1920x-1" through the ambient culture, and ar-SA's negative sign is
not ASCII '-', so the parse failed and the height silently became 0 instead of
-1. Both copies of that parser (App settings targets and the UI settings store)
now parse invariantly.

Audited every remaining culture-sensitive operation in src/ rather than fixing
only what a test happened to catch:

- Numeric Parse/TryParse with no IFormatProvider: 11 sites, all reading
  MACHINE-readable input — env vars (ACDREAM_LIGHT_DEBUG, ACDREAM_NET_DROP_*,
  streaming/quality knobs), CLI arguments, "1920x1080" settings keys, a chat
  command's price argument, and the launcher's bake thread count, which is
  handed straight to a child process command line. All pinned to
  InvariantCulture.
- ToUpper()/ToLower() with no culture: none. The Turkish-I class was already
  clean, and tr-TR confirms it.
- StartsWith/EndsWith/IndexOf(string) with no StringComparison: one —
  ChatInputParser's "@" prefix test, which is a culture-sensitive comparison
  for a single ASCII character. Now the ordinal char overload.

Verified: 13,958 tests pass identically under the machine default, sv-SE,
tr-TR, ar-SA, and de-DE. (The two launcher test assemblies are excluded from
this run only because a running acdream-launcher.exe holds its own binary; the
one launcher change here is the thread-count parse.)

Dates remain on the current culture by intent, unchanged from the previous
commit.

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

src/AcDream.App/Rendering/DisplayModeCatalog.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -134,8 +135,10 @@ internal static class DisplayModeCatalog
             mode = default;
             string[] parts = spec.Split('x', 2);
             if (parts.Length == 2
-                && int.TryParse(parts[0], out int w)
-                && int.TryParse(parts[1], out int h)
+                && int.TryParse(
+                    parts[0], NumberStyles.Integer, CultureInfo.InvariantCulture, out int w)
+                && int.TryParse(
+                    parts[1], NumberStyles.Integer, CultureInfo.InvariantCulture, out int h)
                 && w > 0
                 && h > 0)
             {

src/AcDream.App/Settings/RuntimeSettingsTargets.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System.Linq;
 using AcDream.App.Audio;
 using AcDream.App.Net;
@@ -206,9 +207,14 @@ internal sealed class SilkRuntimeDisplayWindowTarget : IRuntimeDisplayWindowTarg
         if (string.IsNullOrWhiteSpace(spec))
             return false;
         string[] parts = spec.Split('x', 2);
+        // Invariant: a resolution spec is a machine-readable settings key, not
+        // localized input. Parsing it with the ambient culture made "1920x-1"
+        // fail outright under ar-SA, whose negative sign is not ASCII "-".
         return parts.Length == 2
-            && int.TryParse(parts[0], out width)
-            && int.TryParse(parts[1], out height)
+            && int.TryParse(
+                parts[0], NumberStyles.Integer, CultureInfo.InvariantCulture, out width)
+            && int.TryParse(
+                parts[1], NumberStyles.Integer, CultureInfo.InvariantCulture, out height)
             && width > 0
             && height > 0;
     }

src/AcDream.App/Streaming/StreamingDiagnostics.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System;
 
 namespace AcDream.App.Streaming;
@@ -73,5 +74,8 @@ internal static class StreamingDiagnostics
     /// at the parser rather than let the two halves of one commit disagree.
     /// </summary>
     internal static int? ParseRadius(string? raw) =>
-        int.TryParse(raw, out int value) && value >= 1 ? value : null;
+        int.TryParse(raw, NumberStyles.Integer, CultureInfo.InvariantCulture, out int value)
+        && value >= 1
+            ? value
+            : null;
 }

src/AcDream.App/UI/ClientCommandController.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using AcDream.Core.Physics;
 using AcDream.Core.Ui;
 using AcDream.Core.Social;
@@ -724,7 +725,8 @@ public sealed class ClientCommandController
         uint maximumPrice = 0u;
         foreach (string part in parts)
         {
-            if (uint.TryParse(part, out uint price))
+            if (uint.TryParse(
+                    part, NumberStyles.Integer, CultureInfo.InvariantCulture, out uint price))
             {
                 if (price == 0)
                 {