Add configurable structured logging

Adds a leveled JSON logger (error/warn/info/verbose/debug, controlled via
LOG_LEVEL) wired into the Express API (access log, error middleware,
crash handlers, memory heartbeat) and the Next.js server (page-request
proxy, instrumentation crash handlers, heartbeat). LOG_LEVEL is exposed
through compose.yaml, and both services now rotate their Docker logs
(json-file, 20m x 10 files) instead of growing unbounded. Intended to
capture long-running diagnostic data for the intermittent 502s seen on
the Docker host.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/proxy.ts

@@ -0,0 +1,17 @@
+import { NextResponse } from "next/server";
+import type { NextRequest } from "next/server";
+import { createLogger } from "./shared/logging/logger";
+
+const logger = createLogger("web:navigation");
+
+export function proxy(request: NextRequest) {
+  logger.info("page request", {
+    method: request.method,
+    path: request.nextUrl.pathname,
+  });
+  return NextResponse.next();
+}
+
+export const config = {
+  matcher: ["/((?!_next/static|_next/image|favicon.ico|api).*)"],
+};