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/WizardStepLimits.cs

@@ -0,0 +1,17 @@
+namespace GmRelay.Shared.Features.Sessions.CreateSession.Wizard;
+
+/// <summary>
+/// Limits and bounds used by the wizard's input validation. Kept here
+/// (rather than on the Telegram-only <c>WizardStep</c>) so the state
+/// machine can reference them without pulling in a platform dependency.
+/// </summary>
+public static class WizardStepLimits
+{
+    public const int MaxTitleLength = 200;
+    public const int MaxDescriptionLength = 4000;
+    public const int MaxSystemLength = 100;
+    public const int MaxCapacity = 50;
+    public const int MinCapacity = 1;
+    public const int MinDurationHours = 1;
+    public const int MaxDurationHours = 12;
+}