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/agent.rs

@@ -6,15 +6,11 @@
 //! exhausted.
 
 use anyhow::Context;
-use openrouter_rs::{
-    Message,
-    types::{Role, Tool, ToolCall},
-};
 use serde_json::Value;
 use tracing::{debug, warn};
 
 use crate::{
-    open_router::OpenRouterClient,
+    open_router::{Message, OpenRouterClient, Role, Tool, ToolCall},
     sandbox::{Sandbox, tools},
 };
 
@@ -105,10 +101,22 @@ fn parse_args(call: &ToolCall) -> anyhow::Result<Value> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use serde_json::json;
+
+    /// Builds a tool call the way the API returns one, so the fixture also
+    /// covers deserialization.
+    fn tool_call(name: &str, arguments: &str) -> ToolCall {
+        serde_json::from_value(json!({
+            "id": "call_1",
+            "type": "function",
+            "function": { "name": name, "arguments": arguments }
+        }))
+        .unwrap()
+    }
 
     #[test]
     fn parse_args_accepts_empty_arguments() {
-        let call = ToolCall::new("id", "ls", "");
+        let call = tool_call("ls", "");
         assert_eq!(
             parse_args(&call).unwrap(),
             Value::Object(serde_json::Map::new())
@@ -117,13 +125,13 @@ mod tests {
 
     #[test]
     fn parse_args_parses_json_object() {
-        let call = ToolCall::new("id", "ls", r#"{"path":"src"}"#);
+        let call = tool_call("ls", r#"{"path":"src"}"#);
         assert_eq!(parse_args(&call).unwrap()["path"], "src");
     }
 
     #[test]
     fn parse_args_rejects_invalid_json() {
-        let call = ToolCall::new("id", "ls", "not json");
+        let call = tool_call("ls", "not json");
         assert!(parse_args(&call).is_err());
     }
 }