Enhance LLM chat and config

[mcgivrer]

Enhancement of LLM Chat

Chat Auto-scroll (ConversationView)

Problem

scrollToBottom() was triggered before adjustHeight() had resized the WebView, causing incomplete scrolling during streaming.

Fix

An onHeightChanged callback is fired at the end of adjustHeight() in MessageBlock. Scrolling is now driven by this callback rather than being called directly from appendToLastMessage().

LLM Config Change Notification

When the LLM configuration changes (from OptionsDialog or from ContextDialog), the active chat displays a system message:

• MarkNote.showOptionsDialog() calls llmConfig.load() then promptPanel.onConfigChanged() after OptionsDialog closes
• PromptPanel.onConfigChanged() injects a SYSTEM role message into ConversationView with the active model and endpoint
• Dedicated CSS style: pale yellow background #fff8e1, border #ffe082, full width, italic

## ContextDialog — Model Selector

The ⚙ button in PromptInputArea now opens a combined Model + Context dialog:

• Top section: editable ComboBox pre-filled with the current model + Refresh button (calls LLMService.getAvailableModels()) + endpoint label in gray
• Separator
• Bottom section: system context TextArea (existing)
• If the model changes after OK → onConfigChanged() is called → notification posted in the chat.