chore(skeleton): move side-effects-cache flag into pnpm-workspace.yaml

Drops the skeleton .npmrc in favor of the sideEffectsCache: false setting
in pnpm-workspace.yaml. Same behavior, one less file in generated
projects.

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

Author: DASPRiD

skeleton/.npmrc

@@ -1,3 +1,4 @@
+sideEffectsCache: false
 allowBuilds:
   '@biomejs/biome': true
   '@swc/core': true