[Bug] NullPointerException on startup when Vault has no economy provider #79

Bug description

EzShops crashes on startup with a NullPointerException when Vault is installed but no economy provider (e.g. EssentialsX, CMI) has registered a Vault Economy service.

java.lang.NullPointerException: economy
    at com.skyblockexp.ezshops.bootstrap.PlayerShopComponent.<init>(PlayerShopComponent.java:58)
    at com.skyblockexp.ezshops.bootstrap.EzShopsBootstrap.start(EzShopsBootstrap.java:99)

Root cause

EzShopsBootstrap.setupEconomy() has a fallback that returns true when getPlugin("Vault") != null, even when getRegistration(Economy.class) == null:

if (getRegistration(Economy.class) == null && getPlugin("Vault") == null) return false;
// ...
economy = registration.getProvider(); // registration is null -> NPE later
return true;

The economy field stays null, and PlayerShopComponent's constructor throws on Objects.requireNonNull(economy).

Expected behaviour

Like the existing missing-Vault case, the plugin should log a clear message ("no Vault economy provider registered") and disable itself cleanly, instead of crashing with an unhandled NPE.

Fix

Branch fix/bootstrap-economy-npe on fork OrzMC/EzShops:

• setupEconomy() checks getRegistration(Economy.class) first and returns false (clean disable) when no provider is registered, with a helpful log line.
• Adds regression tests covering both "provider registered" and "Vault present but no provider" (MockBukkit).
• While touching PlayerShopComponent, the non-fatal DB-fallback logs (Jaloquent / MySQL) are downgraded from SEVERE to WARNING so a missing remote DB no longer logs at error level.