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/handlers_shell_chat.go

@@ -83,12 +83,12 @@ func (s *Server) buildShellSystemPrompt(req ShellChatRequest) string {
 		sb.WriteString("User: " + user + "\n")
 	}
 
-	isRoot := os.Geteuid() == 0
-	sb.WriteString(fmt.Sprintf("Root: %t\n", isRoot))
-	if isRoot {
-		sb.WriteString("⚠️ Session en root — toutes les commandes ont les privilèges administrateur.\n")
+	canSudo := !agent.NeedsSudoPassword()
+	sb.WriteString(fmt.Sprintf("Root: %t\n", !canSudo))
+	if canSudo {
+		sb.WriteString("⚠️ Session avec privilèges sudo sans mot de passe — les commandes sudo s'exécuteront directement.\n")
 	} else {
-		sb.WriteString("⚠️ Session utilisateur standard — les commandes sudo/doas nécessitent une autorisation. N'utilise PAS sudo ou doas sans demander.\n")
+		sb.WriteString("⚠️ Session sans sudo sans mot de passe — les commandes sudo/doas nécessitent une autorisation. N'utilise PAS sudo ou doas sans demander.\n")
 	}
 
 	now := time.Now()
@@ -196,7 +196,7 @@ func (s *Server) buildShellContextMessages() []orchestrator.Message {
 		}
 		messages = append(messages, orchestrator.Message{
 			Role:    role,
-			Content: content,
+			Content: orchestrator.TextContent(content),
 		})
 	}