chore: drop the redundant @webjsdev/ui pin from scaffolded apps

[vivek7405]

Problem

webjs create pins @webjsdev/ui as a devDependency in generated apps, but the app never imports it at runtime: the UI kit uses the shadcn copy-in model (webjs ui add copies component source into components/ui/, and those files import @webjsdev/core + ../lib/utils.ts, not the kit). The webjs ui command resolves @webjsdev/ui from the CLI's own node_modules (the CLI hard-depends on it), so the app pin is dead weight.

Change

• Remove '@webjsdev/ui' from the generated package.json (create.js).
• Update the scaffold-integration test + any scaffold docs that reference the pin.
• Verify webjs ui add <name> still works in a freshly scaffolded app (resolves the kit from the CLI).

Acceptance criteria

• A generated app has no @webjsdev/ui in its dependencies, and webjs ui add button still copies the component in.
• Scaffold tests + docs updated.

Leaves a scaffolded app's @webjsdev/* deps as just core + server + cli (cli stays: it is the dev/prod toolchain). Related to the node_modules-slimming discussion under epic #381.