1.0.74

fix: rewrite heatmap overlay as per-chunk world-aligned textures

Each 20-tile chunk gets its own CanvasTexture sized to match
the chunk's actual world-space extent (including road gaps).
Tiles paint at their correct world-relative pixel position,
fixing the alignment/mapping issues with the single-plane approach.
Chunks with no scored tiles are skipped entirely.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>