feat(bake-sprite): --pixels-per-meter <N> embeds atlas_meta in sprites.uv.json

Sprite-mode bake gains an additive --pixels-per-meter flag. When set,
the value is written into sprites.uv.json under atlas_meta.
pixels_per_meter. Consumers (lib-core.render path-1 via per-entity
sprite_scale) divide their project canonical px/m by this number to
auto-scale the rendered quad — atlas-native resolution no longer needs
to match the project tile-scale.

Unset (legacy bakes): atlas_meta omitted, byte-equal to v0.3.0 output.

Tests: 53/53 pass; existing buildUvJson test continues to assert the
unset-default shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "sporel-tool-atlas-baker",
-  "version": "0.3.0",
-  "description": "Bake paired diffuse + height PNG atlases for the Sporel map-lib v0.3.0+ format. v0.2: edge-replicated padding (Rev 4 §13.3), --schema blob-14 E1 slot validation, collision.json sidecar E2 validation + pass-through, alpha-analysis opaque flag. Accepts PNG/WebP/JPG via jimp; v0.3 adds --mode sprite for diffuse-only atlases of irregularly-sized sprites with alias→UV-table sidecar",
+  "version": "0.4.0",
+  "description": "Bake paired diffuse + height PNG atlases for the Sporel map-lib v0.3.0+ format. v0.2: edge-replicated padding (Rev 4 §13.3), --schema blob-14 E1 slot validation, collision.json sidecar E2 validation + pass-through, alpha-analysis opaque flag. Accepts PNG/WebP/JPG via jimp; v0.3 adds --mode sprite for diffuse-only atlases of irregularly-sized sprites with alias→UV-table sidecar; v0.4 adds --pixels-per-meter <N> to sprite-mode, embedded as atlas_meta.pixels_per_meter in sprites.uv.json (consumed by render-side scale-resolution per project canonical px/m).",
   "bin": {
     "sporel-atlas-baker": "bin/atlas-baker.js"
   },