refactor(wizard): move core to Shared, add IWizardMessenger contract (issue #112)

Moves the game-creation wizard state machine, view builder, and
platform-neutral contracts (callback data, step names, storage
exception, club option, step limits) from GmRelay.Bot to GmRelay.Shared.
Telegram continues to work through a new TelegramWizardMessenger
implementing IWizardMessenger and a WizardInteractionMapper that
converts Update → WizardInteraction. Wires the new platform column on
wizard_drafts (V032 migration) and switches chat/owner/thread/message
ids to TEXT so the same table can hold Discord snowflakes later.

- GameCreationWizard: now in Shared, takes IWizardMessenger +
  IWizardDraftRepository, dispatches on WizardInteraction.
- New IWizardMessenger contract with Edit/Send/Answer/GetOwnerClubs
  (returns string ids so Telegram longs and Discord snowflakes both
  fit).
- New WizardStepViewBuilder in Shared returns
  (text, IReadOnlyList<WizardAction>); TelegramWizardMessenger
  renders actions into InlineKeyboardMarkup via a new Bot-side
  ToInlineKeyboard helper.
- New WizardInteractionMapper in Bot (5-case test) converts Telegram
  Update to WizardInteraction.
- WizardDraft gains a Platform column; ChatId/MessageThreadId/OwnerId/
  DraftMessageId switched to string. V032 migrates existing rows and
  rebuilds the owner lookup index on (platform, owner_id).
- All existing wizard / create-session tests updated to the new
  contract (HandleInteractionAsync + WizardInteraction). Wizard
  callback-data format preserved.
- dotnet build clean, dotnet format --verify-no-changes clean, all
  101 wizard tests pass.

src/GmRelay.Shared/Features/Sessions/CreateSession/Wizard/WizardStepNames.cs

@@ -0,0 +1,30 @@
+namespace GmRelay.Shared.Features.Sessions.CreateSession.Wizard;
+
+/// <summary>
+/// Symbolic step identifiers used by <see cref="WizardDraft.Step"/> and
+/// the <see cref="WizardCallbackData"/> payload. Strings (rather than an
+/// enum) so that future platforms can extend the set without breaking
+/// the wire format stored in PostgreSQL.
+/// </summary>
+public static class WizardStepNames
+{
+    public const string Type = "Type";
+    public const string Title = "Title";
+    public const string Description = "Description";
+    public const string Cover = "Cover";
+    public const string System = "System";
+    public const string Duration = "Duration";
+    public const string DateTime = "DateTime";
+    public const string Capacity = "Capacity";
+    public const string Visibility = "Visibility";
+    public const string PickClub = "PickClub";
+    public const string Publish = "Publish";
+    public const string Confirm = "Confirm";
+
+    // Pool steps
+    public const string PoolSystemDuration = "PoolSystemDuration";
+    public const string PoolAddSlots = "PoolAddSlots";
+    public const string PoolSlotDateTime = "PoolSlotDateTime";
+    public const string PoolSlotCapacity = "PoolSlotCapacity";
+    public const string PoolConfirm = "PoolConfirm";
+}