feat: add configurable timeout for public database TCP proxy

Adds a per-database 'Proxy Timeout' setting for publicly exposed databases.
The nginx stream proxy_timeout can now be configured in the UI, defaulting
to 3600s (1 hour) instead of nginx's 10min default. Set to 0 for no timeout.

Fixes #7743

app/Models/StandaloneKeydb.php

@@ -19,6 +19,7 @@ class StandaloneKeydb extends BaseModel
 
     protected $casts = [
         'keydb_password' => 'encrypted',
+        'public_port_timeout' => 'integer',
         'restart_count' => 'integer',
         'last_restart_at' => 'datetime',
         'last_restart_type' => 'string',