Release build copies working-tree CSS over the compiled output #55

Found while fixing #53.

In build:release mode, less/sass write compressed CSS to tmp/ and (since #54) minifyCss writes the .min.css siblings there. The copy task then runs with the pattern **/!(*.js|*.jsx|*.less) from the plugin root, which matches the working tree's own css/*.css and css/*.min.css and copies them into tmp/ over the compiled files.

On a fresh clone there is nothing to copy, so the zip is correct. On a developer checkout that has run build:dev, the zip ships whatever CSS that checkout holds: the uncompressed dev build, and stale if the LESS changed after the last build:dev. That is the case for every release built from a working machine rather than CI.

Fix direction: exclude config.css.src (and its .min variants) from the copy glob, or run copy before less/sass/minifyCss so the compiled output wins. Either way verifyCss from #54 should be extended to check that the shipped CSS is the compressed tmp/ output, not a working-tree copy (a size or content check against the working tree would do).