fix: reconcile WalletContext cached address against live Freighter state (#71)

[rafaio1]

Fixes #71.

• Add getActiveFreighterAddress() passive helper to wallet.ts that reads Freighter's current active account without triggering a permission prompt or connect flow.
• Replace WalletContext's bare localStorage mount effect with one that reconciles the cached address against Freighter's live state on mount, surfacing a mismatch: boolean on the context when they diverge.
• Block signing actions in IssueActions.withWallet when mismatch is true, preventing silent identity divergence where the UI shows one address but Freighter signs with another.
• Clear mismatch state on successful reconnect and on disconnect.
• Product decision documented: This fix detects and surfaces the divergence rather than silently auto-updating to the new address. The user must explicitly reconnect, ensuring awareness of which account is being used for signing and payout.
• TypeScript compiles cleanly with npx tsc --noEmit.

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