Set COLORTERM=truecolor in container environment

Tells CLI tools (Claude Code, vim, etc.) that the xterm.js terminal
supports 24-bit RGB color so they use the full palette.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src-tauri/src/docker/container.rs

@@ -120,6 +120,9 @@ pub async fn create_container(
 
     let mut env_vars: Vec<String> = Vec::new();
 
+    // Tell CLI tools the terminal supports 24-bit RGB color
+    env_vars.push("COLORTERM=truecolor".to_string());
+
     // Pass host UID/GID so the entrypoint can remap the container user
     #[cfg(unix)]
     {