pixel-sprite-maker: spritec - .sprite text format -> png/jpg/svg + sprite sheets

- .sprite format: single-char palette keys (hex/rgb()/CSS names/none), grid
  rows, '.' transparent by default, max 256x256 per sprite
- render/sheet/info/preview subcommands; sheets name themselves
  <base>_<cellW>x<cellH>_<cols>x<rows>.<ext> (row-major)
- SVG output RLE-merges pixel runs; JPG composites over --bg
- go tests for parser, colors, scaling, svg, sheet layout

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

pixel-sprite-maker/examples/walk_2.sprite

@@ -0,0 +1,16 @@
+# Frame 2/4 - right leg forward.
+sprite: walk_2
+palette:
+  k = #101018    outline / hair
+  s = #F2C09A    skin
+  b = #2E5FB7    shirt
+  d = #22406E    pants
+grid:
+  ..kkk...
+  ..kss...
+  ..kss...
+  .kbbbk..
+  ..bbb...
+  ..ddd...
+  .d...d..
+  .k...k..