feat(vault): e2e connected-wallet seam (#1591)

[jonybur]

Stacked on #1680 (rebased onto updated #1678). Merge order: #1678 → #1680 → this.

Rescope

#1591 originally asked for provider-selection UI tests. To open the deposit modal you need both wallets connected, and to mock the dApp's data layer you need a stack of GraphQL + contract mocks (Aave config, vault providers, contract reads). The load-bearing piece is the connected-wallet seam - without it nothing in #1591-#1597 can render the deposit-modal at all. This PR ships that seam. The provider-selection UI assertions move to #1592 where the deposit-modal data mocks are introduced.

Production code changes (gated on `NEXT_PUBLIC_E2E_MODE=1`)

• `services/vault/src/context/wallet/VaultWalletConnectionProvider.tsx`: re-enable the `"injectable"` BTC adapter in e2e mode so the wallet-connector picks up the `window.btcwallet` mock.
• `services/vault/src/config/wagmi.ts`: in e2e mode, skip AppKit and build a wagmi config whose only connector is wagmi's `mock`. Push it into wallet-connector's shared singleton via `setSharedWagmiConfig` so AppKitProvider transparently reads from the mock account. Auto-connect on next microtask. `E2E_DEFAULT_ETH_ADDRESS` derived from the test private key in `mockEthWallet.ts`.

Production builds (no NEXT_PUBLIC_E2E_MODE) take the existing AppKit path unchanged.

Test infra

• `e2e/fixtures/connectedWallets.ts` (new): `preConnectWallets({btc, eth})` lands a test in a fully-connected starting state.
• `e2e/connected-state.spec.ts` (new, 2 tests): proves connect button is gone + "Deposit sBTC" CTA renders.
• Updated `DEFAULT_BTC_ADDRESS` in `seededWallets.ts` to a real signet Taproot (P2TR) address derived from the test key, because `AddressTypeProvider` gates the deposit CTA on Taproot.
• Updated `fixtures-smoke.spec.ts` scriptPubKey assertion to match the P2TR shape (5120 + 64 hex).
• Pinned `NEXT_PUBLIC_BTC_NETWORK=signet` in `playwright.config.ts` so the localStorage scope matches what wallet-connector reads.

Acceptance criteria

• Both wallets reach a "connected" state through real wallet-connector code paths
• Provider list populated from the seeded registry, not hardcoded - deferred to e2e: Single-vault deposit happy path #1592 (needs Aave config + contract mocks)
• Selecting a provider enables the next/deposit CTA - deferred to e2e: Single-vault deposit happy path #1592
• Multi-provider selection preserved across re-renders - deferred to e2e: Single-vault deposit happy path #1592
• At-capacity providers disabled - deferred to e2e: Single-vault deposit happy path #1592

Test plan

• `pnpm --filter vault run lint` → 0 errors
• `pnpm --filter vault run test:e2e` on the four new/updated spec files → 15/15 passing