Add HD terrain tile support (64->256px) with legacy-map fallback

[mrkinglollipop]

Summary

Adds HD terrain support by lifting the hardcoded 64px terrain tile resolution to 256px, so terrain textures can be authored/upscaled at 4x. Stock and custom maps continue to work unchanged via a loader-side fallback.

Background

TILE_PIXEL_EXTENT (64) is baked into TileData's fixed-size mip arrays, and WorldHeightMap::countTiles/readTiles integer-divide a source TGA's width by it to infer the tile grid. As a result, simply supplying higher-resolution terrain TGAs does not render sharper — the loader reinterprets the larger image as extra 64px tile variants. Raising the ceiling requires engine changes.

Changes (all in shared Core/GameEngineDevice, so both Generals and Zero Hour build it)

• Bumps TILE_PIXEL_EXTENT 64 -> 256 and the terrain atlas TEXTURE_WIDTH 2048 -> 8192 (within the 16384 Metal/D3D limit).
• Restructures the TileData mip chain from 6 fixed levels (32/16/8/4/2/1) to 8 chained levels (128/64/32/16/8/4/2/1). This is the load-bearing part: a naive constant bump makes the first doMip() write a 128x128 result into the old 32x32 member buffer — a buffer overflow. The chain is rebuilt so each level is exactly half its parent down to 1x1.
• Adds a loader-side fallback in countTiles/readTiles: legacy 64px-grid TGAs are detected (via the caller's INI-declared tile count) and nearest-neighbour expanded to 256px at load, so unmodified base terrain and existing custom maps keep working. HD terrain TGAs simply override the tiles they replace.

Compatibility & cost

• Backward compatible: stock terrain and custom maps render via the fallback path; no map format change.
• Per-terrain-tile working memory grows ~16x (about 21 MB -> 333 MB worst case for a ~1000 distinct-tile map). Acceptable on modern hardware; real maps rarely approach that tile count.

Testing

• Builds clean on macOS arm64 (Apple Silicon), Zero Hour target (build-macos-zh.sh), no new warnings.
• Boot-tested three ways, each ~100s to the shell with zero crash/assert markers: (1) patched engine + stock terrain (exercises the legacy fallback), (2) patched engine + 4x HD terrain pack (native 256px path), (3) full launcher run. Rendered-frame inspection of in-match terrain is still pending on the author's side.
• The buffer-overflow trap noted above was specifically checked for and avoided.

AI-generated code disclosure

Per CONTRIBUTING: this change was developed with substantial LLM assistance (Claude Code) under my direction. Verification performed: full compile on the Zero Hour target, the runtime boot tests above, review of the diff against the engine's terrain/tile data flow, and confirmation the change is comment-and-logic scoped to the terrain tile path. I (the PR author) am responsible for its correctness and have kept the diff readable and commented in the project's // GeneralsX @keyword style. Happy to iterate on anything a maintainer flags.

Cut against the GeneralsX-Beta-13 base.

🤖 Generated with Claude Code