LC²H V4.1.0-BETA

A pretty chunky cleanup update focused on fixing the remaining V4 worldgen issues, making concurrent generation much less cursed and tightening terrain blending across the board xd

• Reworked the concurrent Lost Cities generation path so C2ME/FastChunkGen no longer gets stuck behind BuildingInfo and stripe locks and freezes the server.
• Tightened city-edge terrain blending and kept the terrain shift attached directly to the native NoiseBasedChunkGenerator path, including seam and post-generation cases where smoothing could previously get skipped.
• Fixed underground holes, city underside gaps, ugly mountain/city edges, structure cutoffs, highway blocking and a bunch of concurrent vs serial planner mismatches.
• Hardened cross-chunk deferred tree replay, block attachments, snow reconciliation and floating vegetation cleanup.
• Improved the configurable floating vegetation remover for vines, glow lichen and Immersive Weathering frost, with custom block IDs and automatic frost support when IW is installed.
• Added generation-time chunk tracing, exports and parity checks for terrain and planner decisions so broken generation is much easier to track down.
• Improved Lost Cities 7.5.x grid compatibility and cleaned up a bunch of terrain/planner edge cases.
• Added a lightweight Lost Cities profile preview and improved the config UI, including clipping fixes, input validation and cleaner runtime settings.
• Kept both the Legacy and New layout systems selectable in the UI, with ChaosZPack-style profiles automatically using Legacy where needed.
• Cleaned up old commands, comments, diagnostics and config text.