fix(config): handle tuple-format plugin entries in opencode.json (fixes #3122)

OpenCode supports plugin entries as [string, object] tuples for passing
options, but loadOpencodePlugins assumed all entries were strings.
When a tuple entry hit matchesKnownPlugin, it called .toLowerCase()
on an array, crashing the plugin on startup.

Extract the string name from tuple entries and skip non-string values.
Add regression test covering the tuple plugin format.

assets/oh-my-opencode.schema.json

@@ -36,7 +36,9 @@
           "agent-browser",
           "dev-browser",
           "frontend-ui-ux",
-          "git-master"
+          "git-master",
+          "review-work",
+          "ai-slop-remover"
         ]
       }
     },