[Bug] Importing mcp from opencode creates `opencode.json` if it does not exist

[r1bilski]

If opencode.json does not exist rulesync import --targets opencode --features mcp creates opencode.json file with empty mcp config.

$ ls -la # No opencode.json
total 0
drwxrwxr-x  3 rb   rb     60 Feb 10 18:29 .
drwxrwxrwt 19 root root 1320 Feb 10 18:23 ..

$ npx rulesync import --targets opencode --features mcp
ℹ Importing files from opencode...
ℹ Successfully loaded 1 opencode MCP files
✔ Imported 1 file(s) total (1 MCP files)

$ ls -la # opencode.json got created
total 4
drwxrwxr-x  4 rb   rb    100 Feb 10 18:30 .
drwxrwxrwt 19 root root 1320 Feb 10 18:23 ..
-rw-rw-r--  1 rb   rb     15 Feb 10 18:30 opencode.json
drwxrwxr-x  2 rb   rb     60 Feb 10 18:30 .rulesync

$ cat opencode.json
{
  "mcp": {}
}