Fix slash commands, chat commands, and server_form UI errors

[SjnExe]

• Modified src/core/main.ts to call loadCommands() at startup.
• Modified src/core/events/beforeChatSend.ts to call commandManager.handleChatCommand(event).
• Fixed packs/resource/ui/server_form.json bindings, visibility logic, and renderer type.
• Fixed pre-existing issue in src/core/__tests__/UI.test.ts.

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PR created automatically by Jules for task 14846249216144152681 started by @SjnExe

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