feat: add Stellar onboarding tour

[kaycke1337]

Summary

• add a first-run Stellar onboarding tour with five steps for the send flow
• persist dismissal in localStorage and add a footer restart entry point
• keep tour copy in src/i18n/en.json and anchor the tour to header, wallet, recipient, amount, and submit UI
• add Playwright e2e coverage for completion, restart, Escape dismissal, and refresh persistence

I used a small in-app tour controller instead of adding a tour dependency, keeping the shipped tour code minimal and avoiding another UI overlay package. The overlay does not trap clicks, supports Escape dismissal, restores focus after closing, and respects prefers-reduced-motion for scroll behavior.

Closes #17

Validation

• npx prettier --check .
• npx tsc --noEmit
• git diff --check
• npx vite build
• npx playwright test

Build/test completed successfully. Vite still reports existing dependency/chunk-size warnings from bundled wallet SDK dependencies.

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[truthixify]

The tour itself (OnboardingTour.tsx, 5 steps, dismiss + restart, en.json strings, Playwright e2e) matches #17 well. Same rebase blocker, branched from pre-develop. Rebase, drop reverts to StellarSend/Receive:

git fetch origin
git rebase origin/develop
git push --force-with-lease

Thanks @kaycke1337.