feat: add Fetcher seam with an identifying user agent

src/main/java/dev/marcospaulo/canalhandia/Fetcher.java

@@ -0,0 +1,14 @@
+package dev.marcospaulo.canalhandia;
+
+import java.io.IOException;
+
+/** The one place the plugin talks to the network, so tests can replace it. */
+interface Fetcher {
+
+    /** GET a URL, returning the body. */
+    String get(String url) throws IOException, InterruptedException;
+
+    /** POST JSON with a bearer token, returning the body. */
+    String postJson(String url, String json, String bearer)
+            throws IOException, InterruptedException;
+}

src/main/java/dev/marcospaulo/canalhandia/HttpFetcher.java

@@ -0,0 +1,59 @@
+package dev.marcospaulo.canalhandia;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.charset.StandardCharsets;
+import java.time.Duration;
+
+final class HttpFetcher implements Fetcher {
+
+    /**
+     * pt.minecraft.wiki answers 403 to a default user agent — MediaWiki policy
+     * requires callers to identify themselves.
+     */
+    private static final String AGENT =
+            "Canalhandia-Minecraft-Bot/1.0 (https://marcospaulo.dev.br)";
+
+    private final HttpClient http = HttpClient.newBuilder()
+            .connectTimeout(Duration.ofSeconds(10))
+            .build();
+    private final int timeoutSeconds;
+
+    HttpFetcher(int timeoutSeconds) {
+        this.timeoutSeconds = timeoutSeconds;
+    }
+
+    @Override
+    public String get(String url) throws IOException, InterruptedException {
+        HttpRequest request = HttpRequest.newBuilder(URI.create(url))
+                .timeout(Duration.ofSeconds(timeoutSeconds))
+                .header("User-Agent", AGENT)
+                .GET()
+                .build();
+        return body(http.send(request, HttpResponse.BodyHandlers.ofString()));
+    }
+
+    @Override
+    public String postJson(String url, String json, String bearer)
+            throws IOException, InterruptedException {
+        HttpRequest request = HttpRequest.newBuilder(URI.create(url))
+                .timeout(Duration.ofSeconds(timeoutSeconds))
+                .header("Content-Type", "application/json")
+                .header("User-Agent", AGENT)
+                .header("Authorization", "Bearer " + bearer)
+                .POST(HttpRequest.BodyPublishers.ofString(json, StandardCharsets.UTF_8))
+                .build();
+        return body(http.send(request, HttpResponse.BodyHandlers.ofString()));
+    }
+
+    private String body(HttpResponse<String> response) throws IOException {
+        if (response.statusCode() / 100 != 2) {
+            throw new IOException("HTTP " + response.statusCode() + ": "
+                    + AiText.forLog(response.body()));
+        }
+        return response.body();
+    }
+}