fix: token persistence, context windows, CSS tables/bullets/hr, image attachments

- Fix token count reset on app restart: persist realTokens in conversation.json
- Fix token/context window values: Studio 150K (summarize at 120K), Terminal 100K
- Fix table rendering in terminal tab: correct thead/tbody display model
- Fix copy button always top-right in Studio code blocks
- Add markdown horizontal rule (---) support in Studio and Terminal
- Fix bullet list double dot: remove CSS ::before duplicate bullet point
- Add image attachments support (VLM description, file mentions @file.ext)
- Add sudo detection with cache (sync.Once)
- Fix message content serialization (TextContent wrapper)
- Guide AI to use read_file instead of cat in studio prompt

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

internal/api/chat_engine.go

@@ -92,7 +92,7 @@ func (ce *ChatEngine) RunWithTools(ctx context.Context, messages []orchestrator.
 
 		assistantMsg := orchestrator.Message{
 			Role:      "assistant",
-			Content:   content,
+			Content:   orchestrator.TextContent(content),
 			ToolCalls: choice.Message.ToolCalls,
 		}
 		messages = append(messages, assistantMsg)
@@ -147,7 +147,7 @@ func (ce *ChatEngine) RunWithTools(ctx context.Context, messages []orchestrator.
 
 			messages = append(messages, orchestrator.Message{
 				Role:       "tool",
-				Content:    result.Content,
+				Content:    orchestrator.TextContent(result.Content),
 				ToolCallID: tc.ID,
 				Name:       tc.Function.Name,
 			})
@@ -191,7 +191,7 @@ func (ce *ChatEngine) RunNonStream(ctx context.Context, messages []orchestrator.
 
 		assistantMsg := orchestrator.Message{
 			Role:      "assistant",
-			Content:   content,
+			Content:   orchestrator.TextContent(content),
 			ToolCalls: choice.Message.ToolCalls,
 		}
 		messages = append(messages, assistantMsg)
@@ -213,7 +213,7 @@ func (ce *ChatEngine) RunNonStream(ctx context.Context, messages []orchestrator.
 
 			messages = append(messages, orchestrator.Message{
 				Role:       "tool",
-				Content:    result.Content,
+				Content:    orchestrator.TextContent(result.Content),
 				ToolCallID: tc.ID,
 				Name:       tc.Function.Name,
 			})