Require confirmation before switching the network toggle to mainnet

[defimomof2]

• Switching the wallet network toggle from testnet to public/mainnet in connect-button.tsx now opens the existing ConfirmDialog instead of switching on a single click. The dialog explains that mainnet uses real funds and different contract addresses, that testnet balances won't carry over, and that transactions go to the live network and can't be reversed; the action is styled destructive and requires an explicit "Switch to Mainnet". Switching back to testnet stays one click (lower risk), and the current network is already shown in the wallet button badge and the menu row. Not type-checked or run locally (dependencies were not installed for this quick pass); it only composes existing components with their typed props. Closes Network toggle to mainnet has no confirmation dialog #443
• [ ]Closes Quiz does not enforce time limit despite Quiz.timeLimitMinutes existing #441 — Quiz does not enforce time limit despite Quiz.timeLimitMinutes existing — to be completed
• Closes Wallet network switch does not invalidate cached data #436 — Wallet network switch does not invalidate cached data — to be completed
• Closes Double error notification on reward claim failure #435 — Double error notification on reward claim failure — to be completed

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