Add hands-on tutorial: CIP-30 wallet connect and first preview transaction (Mesh)

## Problem
The Tutorials section currently has essentially one real hands-on guide (`local-cardano-payment-detector`). Newcomers who want a browser + wallet dApp path still hit a thin tutorials area (#115). The old Tools stub page was removed (#191), so we also need a clear “start building a dApp” entry that points at widely used tooling such as Mesh.

## Proposed solution
Add a second tutorial that walks through:

1. Connect a CIP-30 browser wallet
2. Build a simple payment transaction with Mesh (or equivalent maintained TS SDK)
3. Sign and submit on **preview** testnet
4. Confirm on an explorer
5. Short troubleshooting (network mismatch, missing collateral, API keys)

Include links to Mesh docs, faucet, and DevEx Getting Started.

## Acceptance criteria
- [ ] New tutorial page under `website/docs/tutorials/`
- [ ] Listed in Tutorials navigation / Getting Started
- [ ] Uses preview testnet (no mainnet funds required)
- [ ] Clear prerequisites and copy-pasteable steps
- [ ] `npm run build` succeeds

## Related
- #115
- #191 (tools stub removed; this helps replace that entry path)

Start by comparing the existing local-cardano-payment-detector tutorial with the content under website/docs/tutorials/. Add the new tutorial and update Tutorials navigation or Getting Started with links to Mesh docs, the faucet, and DevEx Getting Started. Done means the guide covers CIP-30 connection, a Mesh preview transaction, signing, submission, explorer confirmation, and troubleshooting, and npm run build succeeds.

Vom Indexierungsmodell aus dem Issue-Text verfasst.