fix(mcp): validate action parameter before database check in mobile_inspect_trace

[Mahesh-Abeykoon]

Summary

Validates the action parameter at the start of mobile_inspect_trace before checking if the trace database file exists on disk.

Problem

Previously, mobile_inspect_trace checked for data_engine.db on disk before validating the requested action.

When an unsupported action was passed in an environment where no trace database existed yet (such as on a fresh clone or in an isolated test run), the function returned:

{
  "error": "Database not found",
  "message": "Data engine database does not exist at ... yet."
}