fix(console-log): initialize capture at server boot + prevent SSE proxy buffering

Initialize initConsoleLogCapture() via Next.js instrumentation register()
hook so logs are captured from startup in headless/Docker deployments, and
add X-Accel-Buffering/Cache-Control headers to the SSE stream route to
prevent reverse proxies from buffering the initial payload.

src/instrumentation.js

@@ -0,0 +1,6 @@
+export async function register() {
+  if (process.env.NEXT_RUNTIME === "nodejs") {
+    const { initConsoleLogCapture } = await import("@/lib/consoleLogBuffer");
+    initConsoleLogCapture();
+  }
+}