Replace openrouter-rs with in-tree client and require sandbox

Remove the openrouter-rs dependency in favor of a minimal in-tree
OpenRouter chat-completions client, and drop the BOT_NAME and
SANDBOX_ENABLED config options. Reviews now always run inside the
sandbox, and the review prompt asks the model to read files with the
available tools instead of embedding the diff.

crates/herald-server/src/main.rs

@@ -79,15 +79,14 @@ async fn run() -> anyhow::Result<()> {
     let shutdown = CancellationToken::new();
 
     let sandbox = SandboxConfig {
-        enabled: config.sandbox_enabled,
         runtime: devcontainer_rs::ContainerRuntime::new(config.container_runtime.clone()),
         max_iterations: config.sandbox_max_iterations,
     };
 
-    if sandbox.enabled && !sandbox.runtime.available().await {
+    if !sandbox.runtime.available().await {
         warn!(
             runtime = sandbox.runtime.program(),
-            "Sandbox is enabled but the container runtime is not available"
+            "Container runtime is not available, every review will fail"
         );
     }
 
@@ -95,7 +94,6 @@ async fn run() -> anyhow::Result<()> {
         gitea_user.login,
         gitea_api,
         open_router_client,
-        reqwest::Client::new(),
         config.bot_max_concurrent,
         config.open_router_model.clone(),
         sandbox,