fix(explorer): route gasless Add Service users to Add Funds

[!IMPORTANT]
Current execution is tracked by #436. This issue owns the gasless Add Service return-to-Add-Funds flow in PR #419, after #397 / PR #418. It does not absorb the broader cross-method amount-persistence work deferred from #394. Historical references below are retained for attribution.

Parent tracker: #393
Depends on: #394 and #377

Problem

Submitting Add Service without enough FIL fails at the wallet. The console should route the user to the same funding flow that can add transaction-fee FIL, then return them to the intended Add Service operation.

Scope

• Reuse the shared FIL-sufficiency decision from #377.
• Disable submission while the connected account lacks usable transaction-fee FIL.
• Launch the unified Add Funds host with the FIL option visible.
• Preserve the Add Service form and return action.

Acceptance criteria

• An insufficient-FIL wallet cannot submit the transaction.
• The recovery action opens the unified funding host.
• A wallet/account change cannot resume the old form against the new owner.
• After FIL arrives and balances refresh, the intended operation can be retried.
• Component tests cover sufficient, insufficient, loading, unreadable, cancellation, and account-switch states.
• Repository-required checks pass.

Performance classification: not performance-relevant.

Start at the Add Service flow and inspect the shared FIL-sufficiency decision from #377, the unified Add Funds host, and the existing return action. Run the component tests covering sufficient, insufficient, loading, unreadable, cancellation, and account-switch states. Done means blocked gasless submissions recover through Add Funds and can safely retry the intended operation after funding.