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.Bot/Migrations/V032__wizard_drafts_platform.sql

@@ -0,0 +1,40 @@
+-- V032: Platform-neutral wizard drafts (issue #112).
+-- Adds the platform discriminator and switches owner/chat/thread/message
+-- columns from numeric to TEXT so the same table can hold both Telegram
+-- ids (long) and Discord snowflakes (ulong). All conversions are safe:
+-- the affected columns are nullable except chat_id/owner_telegram_id
+-- which we cast via TEXT.
+
+ALTER TABLE wizard_drafts
+    ADD COLUMN platform TEXT NOT NULL DEFAULT 'Telegram';
+
+-- Convert chat_id: BIGINT → TEXT. Existing rows hold Telegram chat ids
+-- which convert losslessly to their decimal string form.
+ALTER TABLE wizard_drafts
+    ALTER COLUMN chat_id TYPE TEXT USING chat_id::TEXT;
+
+-- Convert message_thread_id: INT (nullable) → TEXT (nullable).
+ALTER TABLE wizard_drafts
+    ALTER COLUMN message_thread_id TYPE TEXT USING message_thread_id::TEXT;
+
+-- Convert draft_message_id: BIGINT (nullable) → TEXT (nullable).
+ALTER TABLE wizard_drafts
+    ALTER COLUMN draft_message_id TYPE TEXT USING draft_message_id::TEXT;
+
+-- Rename owner_telegram_id → owner_id (now platform-agnostic) and
+-- convert from BIGINT to TEXT.
+ALTER TABLE wizard_drafts
+    RENAME COLUMN owner_telegram_id TO owner_id;
+
+ALTER TABLE wizard_drafts
+    ALTER COLUMN owner_id TYPE TEXT USING owner_id::TEXT;
+
+-- Replace the old owner lookup index with one that uses the new column
+-- names and the platform discriminator.
+DROP INDEX IF EXISTS idx_wizard_drafts_owner;
+
+CREATE INDEX idx_wizard_drafts_owner
+    ON wizard_drafts(platform, owner_id);
+
+CREATE INDEX idx_wizard_drafts_platform
+    ON wizard_drafts(platform);