gateway/tools: collapse ToolRegistry::new() and new_with_defaults() into one

Two constructors existed with a subtle trap:

  - `new()` had `#[allow(dead_code)]` and called `register_defaults()`
    via `tokio::task::block_in_place(...)` — a sync wrapper hack around
    an async method, fragile and unused.
  - `new_with_defaults()` was misleadingly named — it created the empty
    registry WITHOUT registering defaults, despite the name.

main.rs was doing the right thing: `new_with_defaults()` + explicit
`.register_defaults().await`. The misleading name was a landmine
for future callers.

Fix: delete the dead `new()` with its block_in_place hack, rename
`new_with_defaults()` → `new()` (Rust idiom — `new` is the canonical
constructor), add a docstring that says what you need to do after.
Single clear API.

Update the one caller in main.rs. Workspace warnings still at 0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/gateway/src/main.rs

@@ -191,7 +191,7 @@ async fn main() {
         .nest("/journal", journald::service::router(journal))
         .nest("/access", access_service::router(access))
         .nest("/tools", tools::service::router({
-            let tool_reg = tools::registry::ToolRegistry::new_with_defaults();
+            let tool_reg = tools::registry::ToolRegistry::new();
             tool_reg.register_defaults().await;
             tools::ToolState {
                 registry: tool_reg,

crates/gateway/src/tools/registry.rs

@@ -67,25 +67,14 @@ pub struct ToolRegistry {
 }
 
 impl ToolRegistry {
-    #[allow(dead_code)]
+    /// Build an empty registry. Callers in an async context should follow
+    /// this with `.register_defaults().await` if they want the built-in
+    /// staffing tools pre-installed — main.rs does exactly that.
     pub fn new() -> Self {
-        let registry = Self {
+        Self {
             tools: Arc::new(RwLock::new(HashMap::new())),
             audit_log: Arc::new(RwLock::new(Vec::new())),
-        };
-        // Register built-in staffing tools
-        tokio::task::block_in_place(|| {
-            tokio::runtime::Handle::current().block_on(registry.register_defaults())
-        });
-        registry
         }
-
-    pub fn new_with_defaults() -> Self {
-        let registry = Self {
-            tools: Arc::new(RwLock::new(HashMap::new())),
-            audit_log: Arc::new(RwLock::new(Vec::new())),
-        };
-        registry
     }
 
     /// Register default staffing tools.