Task: Implement the STL Tiles feature

TASK-DESCRIPTION

Implement feature prompts/features/03-stl-tiles.md (STL Tiles) in scripts/stl-tiles-build.sh plus a Python module scripts/stl_tiles_build.py that the script drives.

The build renders the Earth’s surface from the ETOPO 2022 source tiles (/datasets/dataset-etopo-2022/, read-only) into watertight binary-STL tiles in dataflow.out/stl/ with a manifest, a --check validation mode, and subset rendering (--tiles, --region).

TASK-CONTEXT

• The geometry decisions are recorded in documents/05-stl-approach.md: spherical patch tiles, latitude bands (default 30 degrees) with longitude split by round(360 * cos(mid_lat) / band), single polar-cap tiles, tile-local frame with up = sphere normal at tile center, flat bottom translated to z = 0, base 3 mm + relief 20 mm over the global ETOPO elevation range, 0.25-degree samples with longitude spacing scaled by 1 / cos(mid_lat), globe radius 100 mm.
• The shell script owns the log file and the GDAL VRT over the source tiles; the Python module owns the tiling math, per-tile sampling (average resampling via osgeo.gdal.Warp), mesh construction, STL writing, manifest, and --check validation.
• The tiling/geometry math must be importable without osgeo or numpy (pure Python), so tests/04-stl-tiles-math.sh stays portable.
• Tests: tool-gated tests/03-stl-tiles-build.sh (builds a small region, then validates), portable tests/04-stl-tiles-math.sh (tiling math invariants).

TASK-FILES

• create scripts/stl-tiles-build.sh
• create scripts/stl_tiles_build.py
• create tests/03-stl-tiles-build.sh
• create tests/04-stl-tiles-math.sh
• modify Makefile (wire build and check targets)
• modify scripts/site-state-fetch.sh (STL tile state keys for the dashboard)
• modify TODO.md (mark the STL tile tasks complete after verification)

TASK-OUTPUT

• Implement the files, then run make build, make check, and make test from the repository root.
• Report the tile counts, sizes, and verification results.