[Frontend] Add hydration-safe wallet connection state

## Problem
Wallet state is client-only, so server-rendered markup can disagree with the hydrated UI and show the wrong network or account briefly.
## Acceptance criteria
- SSR output is deterministic and does not claim a connected account before hydration.
- Network/account changes are reflected atomically across dependent components.
- No transaction controls are enabled during an unknown state.
- Tests cover refresh, slow wallet injection, network switch, and rejected connection.

Start by tracing the client-only wallet state through SSR, hydration, and its dependent components, then locate the existing test entry points. Done means deterministic SSR, atomic network and account updates, disabled transaction controls during unknown state, and coverage for refresh, slow wallet injection, network switching, and rejected connections.

Written by the indexing model from the issue text.