fix(health): align Agent readiness contract

src/server.ts

@@ -45,6 +45,8 @@ app.get("/health", async (_req, res) => {
     const runtime = await opencodeRuntime.health();
     res.json({
       ok: true,
+      ready: true,
+      warmed_up: true,
       runtime,
       sessions: sessionBridge.count(),
     });
@@ -52,6 +54,8 @@ app.get("/health", async (_req, res) => {
     const detail = error instanceof Error ? error.message : String(error);
     res.status(503).json({
       ok: false,
+      ready: false,
+      warmed_up: true,
       message: "opencode runtime unavailable",
       detail,
       sessions: sessionBridge.count(),