feat: OpenStreetMap → walkable PSP streetscapes (city3d) + adventure3d floor fix

[doodlewind]

What

A toolchain to bake any real-world location from OpenStreetMap into a textured, walkable PSP 3D scene, plus a fix for a related "black faces" rendering bug in adventure3d.

Built on the existing g3d retained-mesh pipeline — no engine changes; it's all baker + game + assets.

OSM streetscape (feat(city3d))

• framework/bake/fetch-osm.ts — pure-Bun Overpass downloader (multi-endpoint fallback) that vendors the raw JSON under assets/vendor/osm/ (the ODbL source extract, kept for reproducibility + ODbL §4.6).
• framework/bake/bake-osm.ts — projects lat/lon → metres, extrudes building footprints (height from height/building:levels) into window-textured walls + ear-clipped roofs, road ribbons and parks, merged into an N×N chunk grid split by texture (facade / pavement / untextured). Emits a base64 assets-osm-*.ts module + per-building collision AABBs + a street spawn + two procedural REPEAT-wrapping textures.
• framework/games/city3d.js — loads the sub-meshes as static, culled Node3Ds (one shared Material per texture), sun + fog, an optional hand-modeled hero landmark, and a skinned soldier with camera-relative movement (the model turns to face the way it walks) + AABB collision. The ground + skybox are small, camera-following tessellated meshes so the PSP GE guard band never drops a huge triangle.
• Locations: Paris / Place de l'Étoile (Arc de Triomphe hero), Shanghai / Lujiazui (the supertall trio — current default), plus Times Square + Shibuya configs. Swap location by changing one import line.
• docs/osm-streetscape-research.md — survey of non-commercial 3D/geo data sources (raw OSM is the only legal offline path; photoreal 3D tiles are streaming-only).

adventure3d floor fix (fix(adventure3d))

The 38 m arena floor was one finite static slab; the chase camera sits 7 m behind the soldier, so near an edge the camera ends off the floor → black void in the foreground. Replaced it with the same camera-following tessellated ground.

Verification

• Runs on PPSSPP at ~60 FPS (Shanghai supertalls with tiled window facades; soldier walks + turns; no black faces).
• bun run test → 22 passed, 0 failed (new city3d golden; adventure3d golden regenerated).
• bun run typecheck clean.
• Builds on the latest normalized-PSP-SDK toolchain (main @ a3597e8).

Notes / follow-ups

• Draft: this is an initial proof-of-concept of the import pipeline.
• mipsel-sony-psp/ SDK and runtime/target/ stay gitignored.
• fps3d's 20 m room box is a latent case of the same finite-floor issue; not touched here.

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