fix(opencode): prevent opencode.json config pollution in workspace

Set OPENCODE_DISABLE_PROJECT_CONFIG=true in all OpenCode invocations
(execute, model discovery, environment test) to stop the OpenCode CLI
from writing an opencode.json file into the project working directory.
Model selection is already passed via the --model CLI flag.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/adapters/opencode-local/src/server/test.ts

@@ -90,6 +90,8 @@ export async function testEnvironment(
     });
   }
 
+  // Prevent OpenCode from writing an opencode.json into the working directory.
+  env.OPENCODE_DISABLE_PROJECT_CONFIG = "true";
   const runtimeEnv = normalizeEnv(ensurePathInEnv({ ...process.env, ...env }));
 
   const cwdInvalid = checks.some((check) => check.code === "opencode_cwd_invalid");