fix(scan): report a --max-duration timeout as partial, not complete

[harshitgavita-07]

bumblebee scan --max-duration <d> stops walking at the deadline and sets timed_out: true, but the trailing scan_summary still says status: "complete". docs/state-model.md tells receivers to promote only status=complete runs, so a truncated snapshot can replace a fuller one.

Reported in #79 (suggested change 1).

What changed:

• runScan sets status to partial (with an error message) when res.TimedOut is true and the status was otherwise complete. timed_out stays in the record.
• The exit code is unchanged (0), as suggested in the issue. Easy to flip if you want a timeout to exit non-zero.
• docs/transport.md widens the partial definition to include a --max-duration stop, as the issue noted it must.

Tests: TestRunScanTimedOutIsPartial runs a real scan with --max-duration 1ns and checks the summary. It fails on main (status=complete) and passes here. TestRunScanCompleteWhenNotTimedOut guards the normal path. go vet, gofmt and go test ./... are clean.

Not covered: the issue also asks whether complete was meant to describe process end rather than coverage. If so, this PR is the wrong call and the docs-only option in the issue applies instead.