disable opencode auto-update feature as we rely on pacman (#4582)

* disable opencode auto-update feature as we rely on pacman

* Refreshing already produces a .bak, so that's enough

---------

Co-authored-by: David Heinemeier Hansson <david@hey.com>

config/opencode/opencode.json

@@ -1,4 +1,5 @@
 {
   "$schema": "https://opencode.ai/config.json",
-  "theme": "system"
+  "theme": "system",
+  "autoupdate": false
 }

migrations/1769616857.sh

@@ -0,0 +1,3 @@
+echo "Turn off opencode's own auto-update feature (we rely on pacman)"
+
+omarchy-refresh-config opencode/opencode.json