Restructure DuskEVM documentation

[HDauven]

Summary

• restructures DuskEVM documentation into four focused page contracts: overview, quickstart, reference, and bridge guide
• updates navigation and internal links, with permanent redirects from the replaced DuskEVM routes
• documents the OP-style withdrawal lifecycle planned in web-wallet #947: initiate, prove, wait, and finalize
• standardizes public documentation on "testnet DUSK" instead of the legacy nDUSK label
• updates BEP20 bridge and ERC20/BEP20 migration estimates from 15 minutes to around one hour
• explains the two user confirmations in DUSK migration: grant permission, then start the migration

Rationale

The previous DuskEVM material mixed product explanation, network reference, deployment instructions, and bridge operations across broad pages. This split gives each page one job:

• the overview explains what DuskEVM is and when to use it
• the quickstart gets a developer to a deployed contract
• the reference holds network and compatibility facts
• the bridge guide follows the wallet workflow

This keeps the main path concise while preserving operational detail where readers need it.

Coordination

The withdrawal section describes the intended Web Wallet behavior after web-wallet #947 lands. This docs change should be published with or after that PR, once its recipient-encoding blocker is resolved.

Validation

• npm run build
• Starlight internal-link validation: all links valid
• local checks for all new routes and both legacy redirects
• rendered checks for bridge lifecycle labels and corrected timing terminology