test: create_wallet/restore_wallet/debug_auth + 2 dashboard cubits (+21 tests)

[TaprootFreak]

Summary

Stage 8 of the coverage push. Adds 21 unit tests across five previously-untested cubits.

Cubit under test	Test file	Cases
`create_wallet/bloc/create_wallet_cubit.dart`	`test/screens/create_wallet/create_wallet_cubit_test.dart`	4
`restore_wallet/cubit/restore_wallet/restore_wallet_cubit.dart`	`test/screens/restore_wallet/restore_wallet_cubit_test.dart`	3
`debug_auth/cubit/debug_auth_cubit.dart`	`test/screens/debug_auth/debug_auth_cubit_test.dart`	7
`dashboard/bloc/balance_cubit.dart`	`test/screens/dashboard/balance_cubit_test.dart`	4
`dashboard/bloc/pending_transactions_cubit.dart`	`test/screens/dashboard/pending_transactions_cubit_test.dart`	3

What each file covers

• create_wallet_cubit: initial hides the seed + has no wallet, `createWallet` stores the new `SoftwareWallet` (pinning the `'Obi-Wallet-Kenobi'` default name), `toggleShowSeed` flips and returns to hidden after two toggles, `toggleShowSeed` preserves the wallet field.
• restore_wallet_cubit: initial state, `restoreWallet` canonicalises mixed whitespace (` x y ` → `x y`) before delegating to `WalletService.restoreWallet`, the interim `isLoading=true` state is observable.
• debug_auth_cubit: seeds `address` + `savedSignature` from the service; empty-address fallback when service has none; `fetchSignMessage` success + error; `authenticate` success + uses-state-address + error.
• balance_cubit: initial zero-balance state shape `(chain, contract, wallet, asset)`; subscribes to `BalanceRepository.watchBalance` on init; emits each pushed balance through the stream; `close()` cancels the subscription cleanly.
• pending_transactions_cubit: initial empty list; emits fetched list on construction; falls back to empty list (not state-error) when the service throws.

Excluded (and why)

• dashboard_bloc + transaction-history sub-cubits + portfolio/price chart cubits — pull in multiple services or larger event-driven flows; would dwarf this PR.
• transaction_history_receipt_cubit / settings_tax_report_cubit — both use `getTemporaryDirectory()` + real `File` IO; needs path_provider platform-channel plumbing.
• sell_, sell_bitbox_, hardware_connect_bitbox_* — Bitbox-coupled or DFX-sell-flow-coupled; held back to avoid review conflicts with fix: keep dashboard buy actions visible #321 area.
• transaction_history_filter_cubit — already covered by test(screens): cover screen cubits/blocs (+37 tests) #327.

Test plan

• `flutter analyze` on the five new files — clean
• `flutter test` — 21 / 21 passing locally
• CI green