docs: consolidate WebClient setup steps

[omerbek]

Closes #106.

Summary

• Add the shared Web Client project setup steps to the setup guide.
• Move the Next.js webpack dev-script requirement into the setup guide.
• Replace repeated setup blocks in Web Client tutorials with links to the shared guide.

Why

The Web Client tutorials repeated the same prerequisites, project creation, SDK install, and Next.js configuration details. Keeping those in one setup page makes the tutorials easier to follow and reduces future maintenance drift.

Testing

• npx prettier --write docs/src/web-client/setup_guide.md docs/src/web-client/create_deploy_tutorial.md docs/src/web-client/creating_multiple_notes_tutorial.md docs/src/web-client/unauthenticated_note_how_to.md docs/src/web-client/counter_contract_tutorial.md docs/src/web-client/foreign_procedure_invocation_tutorial.md
• npm ci in docs/
• npm run build:dev in docs/
• git diff --check