fix: batch 4 — connection pooling, graceful shutdown, email verification UX

- Prisma: connection_limit=10, pool_timeout=30 on DATABASE_URL in both compose files
- Graceful shutdown: SIGTERM/SIGINT forwarded to Node process in docker-entrypoint.sh
- testEmailConnection: replaced real email send with transporter.verify(), simplified UI to single button
- NotificationLog.userId index: confirmed already present, no change needed

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/server/routers/settings.ts

@@ -322,12 +322,11 @@ export const settingsRouter = router({
    * Test email connection
    */
   testEmailConnection: superAdminProcedure
-    .input(z.object({ testEmail: z.string().email() }))
-    .mutation(async ({ ctx, input }) => {
+    .mutation(async () => {
       try {
-        const { sendTestEmail } = await import('@/lib/email')
-        const success = await sendTestEmail(input.testEmail)
-        return { success, error: success ? null : 'Failed to send test email' }
+        const { verifyEmailConnection } = await import('@/lib/email')
+        const success = await verifyEmailConnection()
+        return { success, error: success ? null : 'SMTP connection verification failed' }
       } catch (error) {
         const message = error instanceof Error ? error.message : 'Unknown error'
         return { success: false, error: `Email configuration error: ${message}` }