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/Cargo.toml

@@ -6,14 +6,12 @@ edition = "2024"
 [dependencies]
 reqwest = { workspace = true }
 tokio = { workspace = true }
-tokio-stream = { workspace = true }
 tokio-util = { workspace = true }
 futures-util = { workspace = true }
 serde_json = { workspace = true }
 serde = { workspace = true }
 sentry = { workspace = true }
 sentry-anyhow = { workspace = true }
-openrouter-rs = { workspace = true }
 dotenvy = { workspace = true }
 tower = { workspace = true }
 tower-http = { workspace = true }
@@ -24,7 +22,6 @@ anyhow = { workspace = true }
 thiserror = { workspace = true }
 ring = { workspace = true }
 hex = { workspace = true }
-bytes = { workspace = true }
 metrics = { workspace = true }
 metrics-exporter-prometheus = { workspace = true }
 devcontainer-rs = { path = "../devcontainer-rs" }