feat: convert ssh tunnels into a plugin

drizzle/postgres/0038_cute_vermin.sql

@@ -0,0 +1,5 @@
+-- c2s_tunnel_presets moved to the tunnels plugin, whose first migration renames
+-- it to p_tunnels_presets. Dropping it here would lose every saved preset, so
+-- this only stops drizzle tracking it. SELECT 1 because MySQL rejects an
+-- empty query.
+SELECT 1;

drizzle/postgres/meta/_journal.json

@@ -267,6 +267,13 @@
       "when": 1790189637011,
       "tag": "0037_dizzy_sage",
       "breakpoints": true
+    },
+    {
+      "idx": 38,
+      "version": "7",
+      "when": 1790201004950,
+      "tag": "0038_cute_vermin",
+      "breakpoints": true
     }
   ]
 }