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/sandbox/tools.rs

@@ -10,11 +10,10 @@ use std::path::Path;
 
 use anyhow::{Context, bail};
 use devcontainer_rs::{ExecOutput, normalize};
-use openrouter_rs::types::Tool;
 use serde_json::{Value, json};
 
 use super::Sandbox;
-use crate::gitea::WebhookType;
+use crate::{gitea::WebhookType, open_router::Tool};
 
 /// Tools available to the model for a given webhook action.
 ///
@@ -216,7 +215,6 @@ mod tests {
         WebhookType::Review(ReviewPayload {
             action: "created".to_string(),
             pull_request: PullRequest {
-                diff_url: "https://example.com/diff".to_string(),
                 number: 1,
                 title: "My PR".to_string(),
             },