Add Terms of Service acceptance gate before first transaction

[Ejirowebfi]

Description

TosContext.tsx exists but the ToS acceptance is not enforced before the first on-chain transaction. Users should explicitly accept the disclaimer before spending real XLM.

Tasks

• Show a ToS modal on first wallet connection if not previously accepted
• Store acceptance in localStorage via useLocalStorage
• Block create_token, mint_tokens, and burn calls until ToS is accepted
• Add a unit test for the acceptance gate

Acceptance Criteria

• ToS modal appears on first connection
• Declining the ToS disconnects the wallet
• Accepting persists the decision and does not show the modal again