feat(vault): e2e wallet-connect (#1590)

[jonybur]

Stacked on #1678 (the #1589 fixture scaffold). Merge that first.

Summary

• Pragmatic mock-first scope for e2e: Wallet connect / disconnect / reconnect #1590: BTC injectable wallet wiring + connect-button state tests. Skips ETH/AppKit and the connected-state menu (require Reown mocking; deferred to a follow-up).
• New: services/vault/e2e/fixtures/walletPageInjection.ts (page-side window.btcwallet injector), services/vault/e2e/wallet-connect.spec.ts (5 tests).
• Updates: installWallets fixture now wires window.btcwallet; new mockHealthCheck route helper; narrowed mockVpProxy's rpc route so it stops shadowing eth-rpc.

Acceptance criteria (rescoped)

• BTC injectable mock available pre-page-load (injector + integration tested)
• Connect button visible & enabled in healthy state
• Connect button disabled with geo hint when /health returns 451
• BTC wallet provider methods are deterministic and reproducible
• Deferred: ETH connect/disconnect (AppKit mock follow-up)
• Deferred: connected-state menu + address truncation in DOM (blocks on AppKit)
• Deferred: network mismatch banner (component does not exist in source; would need to be built)
• Deferred: state persistence across reload (depends on connected state working)

Test plan

• `pnpm --filter vault run lint` -> 0 errors
• `pnpm --filter vault run test:e2e wallet-connect.spec.ts` -> 5/5 pass
• Combined run with fixtures-smoke + wallet-mocks -> 13/13 pass; no regression in existing specs