refactor(explorer): unify Add Funds entry points

> [!IMPORTANT]
> Current execution is tracked by #436. This issue now owns the shared Add Funds host and entry-point unification in PR #414, after #381 / PR #413. Entered-amount persistence is not an acceptance criterion for this layer; Add Service return context is owned by #398 / PR #419, while broader cross-method amount persistence remains deferred. Historical references below are retained for attribution.

Parent tracker: #393
Depends on: #381 replacement PR

## Goal

Route every console Add Funds action through one mounted funding host without changing the existing transfer semantics.

## Scope

- Add a single funding launch context and host.
- Route the wallet menu, dashboard funds section, welcome/account-not-found state, and pending-funding affordance through it.
- Keep the existing direct USDFC deposit and guided Squid flow available during migration.
- Preserve entered amount and intended return action when moving between funding choices.

## Non-goals

- New Squid destination execution.
- Additional source tokens or networks.
- FIL top-up logic.
- Card purchases.
- Visual redesign unrelated to funding entry points.

## Acceptance criteria

- [ ] Every supported Add Funds entry opens the same mounted host.
- [ ] Only one funding dialog tree is mounted.
- [ ] Existing direct deposit and guided funding remain usable.
- [ ] Closing and reopening does not leak stale destination or amount state.
- [ ] Component tests cover every launch site and single-host behavior.
- [ ] Repository-required checks pass.

Performance classification: not performance-relevant; this is UI orchestration with no hot-path or storage change.

Start by reviewing the current execution tracked in #436, the shared-host work in PR #414, and the parent tracker #393. Check the wallet menu, dashboard funds section, welcome/account-not-found state, and pending-funding affordance, then verify the acceptance criteria: one mounted host, preserved existing flows, no stale state, coverage for each launch site, and passing repository checks.

Written by the indexing model from the issue text.