polish: drop dead provider_names, clarify status mapping, README prereq

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -6,6 +6,7 @@ numbers across reverse-lookup sites. Providers are sandboxed WASM components.
 ## Usage
 
 ```shell
+$ rustup target add wasm32-wasip2   # once
 $ just run
 $ curl "http://127.0.0.1:8080/api/v1/number/0700000000"
 ```

crates/server/src/service.rs

@@ -42,10 +42,6 @@ impl LookupService {
         }
     }
 
-    pub fn provider_names(&self) -> Vec<&str> {
-        self.providers.iter().map(|p| p.name()).collect()
-    }
-
     /// Run all providers concurrently; one result per provider name.
     pub async fn lookup(&self, number: &str) -> BTreeMap<String, ProviderResult> {
         let tasks = self.providers.iter().map(|provider| {
@@ -91,6 +87,7 @@ async fn run_provider(
         match tokio::task::spawn_blocking(move || provider.requests(&number)).await {
             Ok(Ok(urls)) => urls,
             Ok(Err(error)) => {
+                // Host-side trap; the 4-status API has no better bucket than parse_failed.
                 warn!(provider = %name, %error, "requests() failed");
                 return ProviderResult::ParseFailed;
             }