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

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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
 }