test(lore): restore the characterization tests lost from PR #371 - #372

PR #371 merged at d75cb86, its first commit. The test commit f06cbc9 was
pushed to the branch but GitHub's record of the pull request head never
advanced past d75cb86, so the squash merge took the decomposition without its
tests. f06cbc9 carries zero check runs — CI never executed these tests, and
the five green checks reported on #371 all belong to the pre-test commit.

Nothing was lost: f06cbc9 remained intact on GitHub and these three files are
restored from it verbatim, byte for byte, rather than rewritten.

That leaves develop currently holding the runOnboard and generateManifest
decomposition with no test covering either. This commit closes that gap. It is
also the first time these tests run on Linux and Windows; they assert exact
byte sequences including newlines, which has only been exercised on macOS.

The tests themselves are unchanged from the reviewed commit. Expectations were
hand-derived from the pre-decomposition implementations rather than captured
from the refactored code, and both suites were mutation-checked: a one-space
change to the annotation indent and a "." -> "./" change to the output
directory default each failed exactly the tests that should have failed.

Coverage restored: cmd/lore/lore/onboard 0% -> 25.8%, cmd/lore/lore 12% ->
19.8%. Per-helper blocks: parseLoreOnboardConfig 3/3, newOnboardProvider 5/5,
reportOnboardResult 13/13, writeOnboardManifest 3/3. syncedRegistry (0/6) and
runOnboard itself (0/7) stay uncovered — both are bound to the registry and the
network.

Verified: make test green, zero FAIL or panic lines by count; gofmt clean.
Plan: docs/plans/audit-remediation.md (phase 1b-i).
Issue: #365