feat: [wasm-geotiff-viewer-poc] PoC wasm, in-browser app

[JustCreature]

Proof-of-concept WebAssembly build that runs the terrain renderer in the browser (viewer-only): pick a single GeoTIFF and it raymarches on WebGPU.

What's here

• New standalone web/ crate (excluded from the workspace; own nightly + build-std toolchain) that reuses render_gpu / dem_io / terrain unchanged.
• WebGPU compute raymarcher, SharedArrayBuffer threading via wasm-bindgen-rayon (GeoTIFF parse + normals run on a worker), native <input type=file> + File-API load, WASD/drag fly camera.
• Built with Trunk; cross-origin isolation via a vendored coi-serviceworker so it works on GitHub Pages.

Minimal changes to existing code

• render_gpu: GpuContext::new_async() (the wasm main thread can't block on pollster) + WebGPU-default limits on wasm.
• dem_io: parse_geotiff_auto_reader<R: Read + Seek> to parse in-memory (browser) bytes.
• Root Cargo.toml: exclude = ["web"] so native builds/CI never compile it.

Scope / limits

Viewer-only — no launcher, tier streaming, or HUD. Large tiles are center-cropped to stay under WebGPU's 128 MB storage-binding limit; rendering is on-demand to avoid pinning weak GPUs. web/README.md documents the build/deploy steps and the hard-won wasm-threading link flags.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 89.13043% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/render_gpu/src/context.rs	85.71%	5 Missing ⚠️

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