wip(assembler): M1 round 1 -- manifest format, block contract, bound audit, native Heightfield2D

Luna, M1 round 1 of 4 (plan in Standalone/ASSEMBLER_M1_REPORT.md):
- Versioned fixed-scale world manifest (the shipped plan format) and the Core block
  contract: point evaluation, interval-or-unknown, influence bound, detail envelope, channels.
- Interval audit: 256 boxes / 6,912 samples, 0 missed, 0 unknown; a deliberately false bound
  is detected (negative control).
- Native Heightfield2D with biome input: 4,096-point hash fae2721c052aec5c identical at
  W1/W8/W16; point queries 2.059 ms vs 62.115 ms legacy -- but NOT a match yet (mean density
  error 274 voxels, 2,261 sign mismatches vs the legacy surface). 45 mesh-free Core queries
  match direct evaluation exactly. Existing cave world unchanged (walkability, 64/64 tiles).
- Open: collision readiness, a valid full-view timing (viewer captures were occluded/empty;
  top-down height maps are the only usable pair).
Also carries the design doc's owner decisions (fixed water; player edits unrestricted, route
law for automatic changes only) and three plugin files + BuildHost scripts that earlier round
commits had missed (also fixed on unreal/core-integration as 2574b56).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Research/WorldAssemblerM1/round1-manifest.json

@@ -0,0 +1 @@
+{"schema_version":1,"content_hash":"c87ae279b0e26f53","recipe":{"schema_version":1,"evaluator_version":1,"units_per_voxel":256,"seed":0,"biome_cell_size_q":204800,"biome_warp_q":64000,"biome_warp_wavelength_q":142222,"biome_border_blend_q":30720,"content_hash":"5cc6cfb49073d366","biomes":[{"id":4097,"base_height_q":-549990,"continent_amplitude_q":23040,"continent_wavelength_q":256000,"mountain_amplitude_q":6144,"mountain_wavelength_q":128000,"detail_amplitude_q":512,"detail_wavelength_q":6400},{"id":4098,"base_height_q":-532070,"continent_amplitude_q":40960,"continent_wavelength_q":355556,"mountain_amplitude_q":21504,"mountain_wavelength_q":170667,"detail_amplitude_q":768,"detail_wavelength_q":8000}]},"plan":{"schema_version":1,"content_hash":"9aa8b4c29a69233a","strates":[{"strate_index":1,"top_chunk_z":-16,"bottom_chunk_z":-79,"cap_height_q":-123904,"cap_undulation_q":0,"cap_wavelength_q":131072,"content_hash":"13ba05e186627ed8","features":[],"route":[]}]}}