fix: resolve AppContext memory leak for direct app.express handlers

[sjorobekov]

Problem

Currently, the per-request AppContext cleanup (res.on('close', () => req.originalContext.end())) only happens inside routeInfoMiddleware. This middleware is only attached per-route during setupRoutes.

If consumers register handlers directly on app.express (e.g., app.express.get('/healthz', handler), they bypass setupRoutes. As a result, every request to these bare routes permanently leaks:

• An 'abort' event listener on the long-lived root nodekit.ctx.abortSignal
• An AppContext instance
• An OTel Span

Solution

This PR moves the per-request AppContext cleanup hook from the per-route routeInfoMiddleware into the global setupBaseMiddleware.

Because setupBaseMiddleware is the same place the context is originally created, the cleanup will now reliably run for every request that hits the Express app, regardless of how the handler was registered.