Add model change callback and improve chat UI robustness

- Persist selected model to settings when changed via dropdown
- Reorder chat controls: model selector before mode selector, new chat before delete
- Add null guards for modelSelectorEl during async populate
- Fix streaming state and empty response handling in tool nudge loop
- Expand vault operation keyword detection
- Enable text selection in chat messages
- Include original error message in chat error display

tests/chat-view.test.ts

@@ -121,7 +121,8 @@ describe('ChatView', () => {
       undefined,
       undefined,
       undefined,
-      new ChatHistoryManager()
+      new ChatHistoryManager(),
+      undefined
     );
     // Obsidian's contentEl has a createEl helper that standard DOM lacks
     // Unlike standard DOM, Obsidian elements can create nested elements with createEl
@@ -423,13 +424,11 @@ describe('ChatView', () => {
           })()
         );
 
-      const handleToolSpy = jest
-        .spyOn(view['toolExecutor'], 'handleToolCall')
-        .mockResolvedValue({
-          success: true,
-          message: 'Found vault context',
-          data: [{ path: 'Prompts.md', title: 'Prompts' }],
-        });
+      const handleToolSpy = jest.spyOn(view['toolExecutor'], 'handleToolCall').mockResolvedValue({
+        success: true,
+        message: 'Found vault context',
+        data: [{ path: 'Prompts.md', title: 'Prompts' }],
+      });
       jest.spyOn(view['ollamaClient'], 'chat').mockResolvedValue({
         role: 'assistant',
         content: 'I found vault context and can now suggest the next organization step.',
@@ -441,14 +440,10 @@ describe('ChatView', () => {
 
       expect(handleToolSpy).toHaveBeenCalled();
       expect(
-        handleToolSpy.mock.calls.some(
-          ([toolCall]) => toolCall.function.name === 'get_vault_stats'
-        )
+        handleToolSpy.mock.calls.some(([toolCall]) => toolCall.function.name === 'get_vault_stats')
       ).toBe(true);
       expect(
-        handleToolSpy.mock.calls.some(
-          ([toolCall]) => toolCall.function.name === 'list_vault_tags'
-        )
+        handleToolSpy.mock.calls.some(([toolCall]) => toolCall.function.name === 'list_vault_tags')
       ).toBe(true);
 
       const messages = (view as any).messages;