v0.2.0a16

This one is for platforms running agents for their own customers.

Which customer a run belongs to can come from the environment

SPONSIO_PROJECT names it, so a per-customer credential needs no code
change and cannot get the customer wrong.

Before this, attach() always claimed default. A key scoped to one
customer is refused any other project by name, so it was refused
default too, and runs from a correctly wired deployment never arrived
at all. Anyone handing out per-customer keys needs this release; nothing
older works for that shape.

SPONSIO_API_KEY=sk_...        # the key for this customer
SPONSIO_PROJECT=acme-health   # who they are
SPONSIO_PRIVACY=tool_calls    # what may leave their machine

Passing project= explicitly still wins; the environment is the fallback,
and omitting both keeps the old behaviour.

The OTLP exporter obeys the privacy level

SPONSIO_PRIVACY governed the session upload and not the span exporter,
so a deployment set to send only tool calls could still export argument
values and model text over OTLP. The level you set is now the level that
leaves the machine on either path.

Full diff: v0.2.0a15...v0.2.0a16