Adopt Bake Node for JavaScript packages

[samuel-williams-shopify]

Summary

• add bake-node as a Utopia dependency
• remove Utopia::Components and the utopia:components:update task now that Bake Node owns static package projection
• add Utopia::ImportMap.load_manifest so generated browser mappings are loaded directly without duplicating package.json configuration
• preserve page-relative import paths for static site rendering while leaving external URLs absolute
• migrate the JavaScript integration guide to bake-node.packages and the node:* tasks
• document the 3.0.x migration and regenerate project documentation

Validation

• bundle exec bake test — 483 tests, 1194 assertions
• bundle exec rubocop — no offenses
• bundle exec bake decode:index:coverage lib — 481/481 public definitions documented
• verified node:* tasks are available through the Utopia dependency set