Tag LoadedInstrument with installedAt; process() publishes that field (not a re-read
of reloadGeneration_) so the pruner's displacedAt <= seen bound is airtight. Also fixes
sampleRowHitTest canvas.bottom over-read and adds interleave-stride + canvas-clip tests.
Vendor Steinberg VST3 SDK (v3.7.9_build_61); add reasampler_vst.vst3 as a second, additive build artifact with pure editor-geometry + bridge-marshal helpers under CTest.