chore(debug): add /debug-realtime page + bare SSE endpoint

Tijdelijke debug-tooling voor M8-acceptance op Vercel preview.

- app/api/debug/realtime-stream/route.ts — geen auth, geen filtering;
  dropt elke pg_notify-event op scrum4me_changes rauw door als SSE
- app/debug-realtime/page.tsx — open zonder login op de root, toont
  binnenkomende events in een simpele <table>

Doel: isoleren of de SSE + Postgres LISTEN-pipe op Vercel überhaupt
events laat zien, los van iron-session, productfilter of solo-store.
Als ook deze niets binnen krijgt: probleem zit in pg connection of
Vercel function lifecycle. Als deze wel events toont: probleem zit
hoger in de stack (filter, store, hook).

VERWIJDEREN voordat de PR uit draft gaat.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/api/debug/realtime-stream/route.ts

@@ -0,0 +1,114 @@
+// TIJDELIJKE debug-endpoint voor M8-acceptance.
+// Geen auth, geen filtering — alle pg_notify-events op `scrum4me_changes`
+// stromen rauw door naar de browser. Bedoeld om te isoleren of de
+// SSE + LISTEN-pipe op Vercel werkt, los van iron-session, productfilter
+// of solo-store.
+//
+// VERWIJDEREN VOOR M8 OUT-OF-DRAFT.
+
+import { NextRequest } from 'next/server'
+import { Client } from 'pg'
+
+export const runtime = 'nodejs'
+export const dynamic = 'force-dynamic'
+export const maxDuration = 300
+
+const CHANNEL = 'scrum4me_changes'
+
+export async function GET(request: NextRequest) {
+  const directUrl = process.env.DIRECT_URL ?? process.env.DATABASE_URL
+  if (!directUrl) {
+    return Response.json({ error: 'DIRECT_URL/DATABASE_URL niet gezet' }, { status: 500 })
+  }
+
+  const isPooled = directUrl.includes('pooler.')
+  const hostHint = directUrl.match(/@([^/]+)/)?.[1] ?? 'unknown-host'
+  console.log(`[debug-realtime] connecting (${isPooled ? 'POOLED' : 'direct'}) host=${hostHint}`)
+
+  const encoder = new TextEncoder()
+  const pgClient = new Client({ connectionString: directUrl })
+  let closed = false
+  let heartbeatTimer: ReturnType<typeof setInterval> | null = null
+
+  const stream = new ReadableStream({
+    async start(controller) {
+      const enqueue = (chunk: string) => {
+        if (closed) return
+        try {
+          controller.enqueue(encoder.encode(chunk))
+        } catch {
+          // already closed
+        }
+      }
+
+      const cleanup = async (reason: string) => {
+        if (closed) return
+        closed = true
+        if (heartbeatTimer) clearInterval(heartbeatTimer)
+        try {
+          await pgClient.end()
+        } catch {
+          // ignore
+        }
+        try {
+          controller.close()
+        } catch {
+          // already closed
+        }
+        console.log(`[debug-realtime] closed: ${reason}`)
+      }
+
+      try {
+        await pgClient.connect()
+        await pgClient.query(`LISTEN ${CHANNEL}`)
+        console.log('[debug-realtime] LISTEN ready')
+      } catch (err) {
+        console.error('[debug-realtime] pg connect/listen failed:', err)
+        enqueue(`event: error\ndata: ${JSON.stringify({ message: String(err) })}\n\n`)
+        await cleanup('pg connect failed')
+        return
+      }
+
+      pgClient.on('notification', (msg) => {
+        console.log(`[debug-realtime] RAW notification length=${msg.payload?.length ?? 0}`)
+        if (!msg.payload) return
+        enqueue(`data: ${msg.payload}\n\n`)
+      })
+
+      pgClient.on('error', async (err) => {
+        console.error('[debug-realtime] pg client error:', err)
+        await cleanup('pg error')
+      })
+
+      pgClient.on('end', () => {
+        console.log('[debug-realtime] pg client end')
+      })
+
+      enqueue(
+        `event: ready\ndata: ${JSON.stringify({
+          host: hostHint,
+          pooled: isPooled,
+          channel: CHANNEL,
+          time: new Date().toISOString(),
+        })}\n\n`,
+      )
+
+      heartbeatTimer = setInterval(() => {
+        enqueue(`: heartbeat ${new Date().toISOString()}\n\n`)
+      }, 25_000)
+
+      request.signal.addEventListener('abort', () => {
+        cleanup('client aborted')
+      })
+    },
+  })
+
+  return new Response(stream, {
+    headers: {
+      'Content-Type': 'text/event-stream; charset=utf-8',
+      'Cache-Control': 'no-cache, no-transform',
+      Connection: 'keep-alive',
+      'X-Accel-Buffering': 'no',
+    },
+  })
+}