Add batch operations and merchant cockpit

[Pelafustan-byte]

Summary

• add a per-game-server MoneyRate, propagated through the game context and money distribution
• add a guarded Batch Operations admin page for economy, realm, drop, monster, item, and merchant operations with preview-first workflows
• add a Merchant Cockpit for item search, shop editing, slot ordering, and replace/append shop cloning
• add the EF migration and Admin Panel navigation entries

MoneyRate defaults to 1, including existing database rows, so the feature does not change the current server balance by itself.

Validation

• MUnique.OpenMU.Web.AdminPanel.csproj: builds with 0 errors
• MUnique.OpenMU.Startup.csproj: builds with 0 errors
• package validator: 11/11 checks passed
• Docker deployment and automatic schema update completed; OpenMU and PostgreSQL healthy
• verified all three existing realms retain MoneyRate = 1
• browser-tested Merchant Cockpit search, slot placement, auto-order, copy preview/staging/discard, and a real save/reload/native-editor round trip followed by restoration
• browser-tested Batch Operations against the live configuration without applying a mass operation
• verified existing account and character counts remained unchanged