feat: convert ssh tunnels into a plugin

drizzle/sqlite/0034_curious_molecule_man.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;