Clean up compiler warnings and document Ollama/LiteLLM backends

Remove unused `any_docker_mcp()` function, add `#[allow(unused_imports)]`
and `#[allow(dead_code)]` annotations to suppress false-positive warnings.
Update README.md and HOW-TO-USE.md with Ollama and LiteLLM auth backend
documentation including best-effort compatibility notices.

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

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

@@ -22,6 +22,7 @@ impl ExecSession {
             .map_err(|e| format!("Failed to send input: {}", e))
     }
 
+    #[allow(dead_code)]
     pub async fn resize(&self, cols: u16, rows: u16) -> Result<(), String> {
         let docker = get_docker()?;
         docker