fix(discord): address code-review findings on wizard adapter (issue #112)

VERDICT from verifier (D:\Projects\Game\docs\review-report.md):
REQUEST_CHANGES — wizard was functionally broken at runtime.

## Critical

C-1. Choice-button customId was missing the 'choice:' segment.
    ButtonCustomId emitted 'wizard:btn:<step>:<value>' but the
    dispatcher's switch matches parts[1] == 'choice'. Every choice
    button (D&D 5e, Pathfinder, Waitlist, Publish, Confirm) fell
    into the default branch and showed 'Unknown button'.

    Fix: split into 3 customId helpers:
      ChoiceButtonCustomId(step, value)       -> 'wizard:btn:choice:<step>:<value>'
      ControlButtonCustomId(action)            -> 'wizard:btn:<action>:1'  (back/cancel/skip/create)
      ModalTriggerButtonCustomId(modalStep)    -> 'wizard:btn:modal:<modalStep>'
    Bulk-rewrote all 66 Btn() call sites in DiscordWizardStep.cs.

C-2. "Другое…" modal-trigger buttons were unrouted in dispatcher.
    Added 'parts[1] == "modal"' branch that opens the modal via
    InteractionCallback.Modal(BuildModal(parts[2], draft.ChatId)).

C-3. DiscordWizardSubmitter was leaking ex.Message from
    CreateSessionHandler to the user-visible draft embed. Postgres
    exceptions expose schema/constraint names. Replaced with
    generic user-facing error; full exception still logged
    server-side on the existing catch block.

## I-3 — parser-roundtrip tests (the gap that let C-1/C-2 through)

Added two real behavioural tests (not string-grep) to
DiscordWizardInteractionModuleSourceTests:
  - Renderer_And_Dispatcher_Agree_On_Wire_Format
  - ControlButtons_Are_Parsed_As_Control_Not_Choice
These mirror NetCord's [ComponentInteraction("wizard")] prefix
strip, run the parser, and assert the dispatcher would route to
the right branch. Catches the entire class of 'renderer and
dispatcher disagree on the wire format' regressions.

## I-6 — BuildResumeRow (cascading fix from C-1)

After C-1, BuildResumeRow's ButtonCustomId('cancel', '1') would
emit the wrong format. Switched to direct format strings
('wizard:btn:cancel:1', 'wizard:btn:resume:continue', etc.) which
match the dispatcher's 'back'/'cancel'/'create'/'resume' cases
directly, not the 'choice' prefix.

## Version sync (3.8.0 -> 3.9.0)

Directory.Build.props: <Version>3.9.0</Version>
compose.yaml: all 3 image tags -> 3.9.0
Version_ShouldBeSynchronizedForDiscordFeatureRelease test now green.

## Stats

build: 0 warnings, 0 errors
format: 0 of 279 files need changes
tests: 583 passed, 2 skipped (pre-existing), 0 failed
files: 7 changed, 226 +, 79 -

tests/GmRelay.Bot.Tests/Discord/DiscordWizardInteractionModuleSourceTests.cs

@@ -2,6 +2,7 @@ using System;
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using GmRelay.DiscordBot.Features.Sessions.Wizard;
 
 namespace GmRelay.Bot.Tests.Discord;
 
@@ -177,6 +178,92 @@ public sealed class DiscordWizardInteractionModuleSourceTests
         Assert.Contains("SelectedValues[0]", source, StringComparison.Ordinal);
     }
 
+    /// <summary>
+    /// Roundtrip the renderer output through the dispatcher's parser to
+    /// prove the wire formats agree. This is a real behavioural test
+    /// (not a string-grep) — it actually constructs the ButtonProperties
+    /// that NetCord would send, strips the [ComponentInteraction("wizard")]
+    /// prefix exactly as NetCord does, and asserts the dispatcher's
+    /// switch would route the click to the right branch. Catches the
+    /// class of "renderer and dispatcher disagree on the wire format"
+    /// regressions that the string-grep tests above cannot detect.
+    /// </summary>
+    [Fact]
+    public void Renderer_And_Dispatcher_Agree_On_Wire_Format()
+    {
+        // Choice button: dispatcher expects `btn:choice:<step>:<value>`.
+        var choice = DiscordWizardStep.ChoiceButtonCustomId("Type", "single");
+        Assert.Equal("wizard:btn:choice:Type:single", choice);
+        var choiceArgs = StripWizardPrefix(choice);
+        var choiceParts = choiceArgs.Split(':', 4);
+        Assert.Equal("btn", choiceParts[0]);
+        Assert.Equal("choice", choiceParts[1]);
+        Assert.Equal("Type", choiceParts[2]);
+        Assert.Equal("single", choiceParts[3]);
+
+        // Control button: dispatcher expects `btn:<action>:1`.
+        var cancel = DiscordWizardStep.ControlButtonCustomId("cancel");
+        Assert.Equal("wizard:btn:cancel:1", cancel);
+        var cancelArgs = StripWizardPrefix(cancel);
+        var cancelParts = cancelArgs.Split(':', 3);
+        Assert.Equal("btn", cancelParts[0]);
+        Assert.Equal("cancel", cancelParts[1]);
+
+        // Modal trigger: dispatcher expects `btn:modal:<modalStep>`.
+        var modal = DiscordWizardStep.ModalTriggerButtonCustomId("SystemFreeText");
+        Assert.Equal("wizard:btn:modal:SystemFreeText", modal);
+        var modalArgs = StripWizardPrefix(modal);
+        var modalParts = modalArgs.Split(':', 3);
+        Assert.Equal("btn", modalParts[0]);
+        Assert.Equal("modal", modalParts[1]);
+        Assert.Equal("SystemFreeText", modalParts[2]);
+
+        // All customIds must fit Discord's 100-char limit.
+        Assert.All(
+            new[] { choice, cancel, modal },
+            cid => Assert.True(
+                cid.Length <= DiscordWizardStep.MaxCustomIdLength,
+                $"CustomId '{cid}' exceeds 100 chars: {cid.Length}"));
+    }
+
+    /// <summary>
+    /// The Create/Back/Cancel/Resume control buttons in the renderer
+    /// (and in BuildResumeRow) must emit the format the dispatcher's
+    /// switch matches directly — NOT the choice-button format. This
+    /// test parses every button's customId and asserts the dispatcher
+    /// would route it to the right branch.
+    /// </summary>
+    [Fact]
+    public void ControlButtons_Are_Parsed_As_Control_Not_Choice()
+    {
+        // Real customIds the renderer / BuildResumeRow emit for control actions.
+        var controlIds = new[]
+        {
+            DiscordWizardStep.ControlButtonCustomId("back"),
+            DiscordWizardStep.ControlButtonCustomId("cancel"),
+            "wizard:btn:create:1",
+            "wizard:btn:resume:continue",
+            "wizard:btn:resume:restart",
+        };
+
+        foreach (var cid in controlIds)
+        {
+            var parts = StripWizardPrefix(cid).Split(':', 3);
+            Assert.Equal("btn", parts[0]);
+            // The dispatcher's switch matches these as parts[1] == "back"|"cancel"|"create"|"resume".
+            // They must NOT be tagged as "choice" (that would route through the wizard
+            // with a nonsensical step name).
+            Assert.NotEqual("choice", parts[1]);
+        }
+    }
+
+    /// <summary>Mirror NetCord's [ComponentInteraction("wizard")] prefix strip.</summary>
+    private static string StripWizardPrefix(string customId)
+    {
+        const string prefix = "wizard:";
+        return customId.StartsWith(prefix, StringComparison.Ordinal) ? customId[prefix.Length..] : customId;
+    }
+
     private static int CountOccurrences(string haystack, string needle)
     {
         if (string.IsNullOrEmpty(needle)) return 0;