AI Assistant `search_traces` tool silently overwrites user-provided `error` attribute when `with_errors` is true

[Harizz076]

What happened?

When querying traces using the AI Assistant's search_traces
MCP tool, providing an explicit attributes filter for error
(e.g., "error": "false") alongside with_errors: true results
in the user's manual filter being silently clobbered.

The buildQueryParams function unconditionally sets
attributes["error"] = "true" if WithErrors is enabled,
regardless of whether the user explicitly requested a
conflicting attribute value in the same query. This results
in the backend querying for traces with error=true without
warning the user that their error=false filter was ignored.

Steps to reproduce

1. Invoke the AI Assistant's search_traces tool.

2. Provide a query input that explicitly sets the error
   attribute to "false" while simultaneously setting
   with_errors to true:

   {
   "service_name": "my-service",
   "attributes": {
   "error": "false"
   },
   "with_errors": true
   }

3. Observe that the search executes for traces containing
   errors, completely ignoring the manual error=false filter.

Expected behavior

The system should surface the conflict to the caller rather
than silently choosing a behavior. If with_errors: true is
set, and attributes["error"] is explicitly set to anything
other than "true", the handler should fail fast and return
a clear validation error.

Relevant log output

N/A