Ability to customize the exception-based error messages in the plugins by using message keys rather than strings

Goal

Let plugins throw exceptions that carry a message key resolved against the plugin's messages, instead of a hard-coded human string — e.g. throw new PermissionError("treasury.error.no-permission").

Grounded

Hibernia's CommandManager (hibernia-framework/.../commander/CommandManager.java) already maps its built-in exceptions to fixed keys (NoPermissionException → hibernia.error.no-permission, BadCommandException → hibernia.error.bad-command, plus NotFoundException/ConflictException/ExceedsLimitException) and renders them via the injected Message bean (sendError / handleInvocationFailure, ~lines 489–534). But a thrown exception's own getMessage() is treated as a literal string — there's no way to pass a plugin-specific message key + placeholders.

Fix

• Add a LocalizableException interface exposing getMessageKey() + getPlaceholders().
• In handleInvocationFailure/sendError, if the thrown exception is LocalizableException, resolve its key against the plugin's Message bean (with placeholders) rather than using the raw message.
• Preserve current behaviour for plain exceptions (back-compat).

Acceptance

• A plugin can throw new SomeError(messageKey, placeholders…) and HF renders the resolved, localized message from that plugin's properties.
• Existing built-in error keys still work.