[FEATURE]: send one final telemetry_opted_out event when telemetry is disabled #1499

Describe the enhancement you want to request

Telemetry is on by default and can be turned off with ALTIMATE_TELEMETRY_DISABLED, OPENCODE_DISABLE_TELEMETRY or telemetry.disabled in the user config. A machine that opts out simply goes silent, so on the dashboards an opted-out user looks like a user whose CLI events are missing, and gets debugged as a bug.

Proposal: when telemetry is disabled and the machine has sent telemetry before (a machine id exists), send exactly one final telemetry_opted_out event and then nothing, ever, until telemetry is re-enabled. The event carries the machine id, the CLI version and how the opt-out was set (environment variable or user config). It does not carry the signed-in user id or tenant, so an opt-out doesn't record who opted out; counting opt-outs per machine is enough to explain the silence. A local marker file prevents a repeat; re-enabling telemetry clears the marker so a later opt-out is recorded again.

Opt-outs set before the first launch produce no event, which the dashboard states as an unknowable remainder.

Additional context

Agreed approach for the workspace funnel: the last event sent is the opt-out itself, so missing CLI events after it are explained rather than investigated.