Refactor: Move all UI widget construction to module level

- Extract all QWidget/QLayout instances and property configuration to module level
- Group by element: constructor → properties for each widget
- Keep __init__ assembly-only: addWidget, addLayout, addStretch, signals
- Explicit naming for clarity: separator_vertical_fader_zone_left, etc
- Applies to: IO columns (MIDI IN/OUT, Transport, OSC), Preset Browser, Transport/Fader/Toggle rows, OSC feedback containers
- Pattern: Module = what it is; __init__ = where it goes

presets/presets.json

@@ -1,5 +1,5 @@
 {
-  "__last_used__": null,
+  "__last_used__": "gay3",
   "presets": {
     "1": {
       "midi_port": "IAC Driver Bus 1",
@@ -1027,7 +1027,7 @@
           "hw_cc": null,
           "output_mode": "osc",
           "osc_addr": "/play",
-          "trigger_mode": "momentary"
+          "trigger_mode": "toggle"
         },
         {
           "uid": "e2e8eb84-c2c9-4060-a818-b087ebd5aabd",
@@ -1041,7 +1041,7 @@
           "hw_cc": null,
           "output_mode": "osc",
           "osc_addr": "/play",
-          "trigger_mode": "momentary"
+          "trigger_mode": "toggle"
         },
         {
           "uid": "6b5bcaf7-1d01-4ccd-b23a-ebae8da57a7f",
@@ -1055,7 +1055,7 @@
           "hw_cc": null,
           "output_mode": "osc",
           "osc_addr": "/play",
-          "trigger_mode": "momentary"
+          "trigger_mode": "toggle"
         },
         {
           "uid": "2a1fcb50-b9f2-4c33-bce0-5bd5cadd9c46",
@@ -1069,7 +1069,7 @@
           "hw_cc": null,
           "output_mode": "osc",
           "osc_addr": "/play",
-          "trigger_mode": "momentary"
+          "trigger_mode": "toggle"
         }
       ],
       "browser": {