Reverts 259 files that carried unrelated upstream changes through the
phase-6 merge: enum class removals (cppcoreguidelines-use-enum-class),
scoped_lock→lock_guard conversions (modernize-use-scoped-lock),
nodestore Backend API changes (void const* key), .clang-tidy config,
test infrastructure deletions, and miscellaneous develop changes.
These changes belong on develop, not in the telemetry PR chain.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>