Tier 2: cross-repo tracking issue for `bitbox-testkit` scenarios

[TaprootFreak]

Context

#548 (Tier 2 BitBox simulator coverage) needs new scenarios in DFXswiss/bitbox-testkit. The work cannot land in DFXswiss/realunit-app alone — it's a cross-repo workflow:

1. PR in DFXswiss/bitbox-testkit adding the scenario(s) under go/bitbox/simulator/scenarios.go
2. Tag a new testkit release (v0.5.1 or v0.6.0)
3. Bump the action ref pin on .github/workflows/bitbox-simulator.yml:72 here

This issue is a placeholder to track the cross-repo dependency from this side. The actual scenario PR happens in DFXswiss/bitbox-testkit.

Scope

• Open the matching tracking issue in DFXswiss/bitbox-testkit with the scenario list from Tier 2: extend BitBox02 firmware simulator beyond hardware_connect_bitbox #548 (in scope: SellBitboxEIP1559RealUnitTx, SellBitboxFailureBranches, EthAddressRealUnitMainnetExact, EthAddressRealUnitSepoliaExact)
• Link this issue to the bitbox-testkit tracker (cross-repo via URL)
• Close this when the testkit PR + release + action-pin bump have all landed

Acceptance criteria

• A bitbox-testkit issue exists referencing the four scenarios
• The action-pin in .github/workflows/bitbox-simulator.yml:72 has been bumped to the release that includes them
• This issue closes when the bump PR merges here

Estimated effort

Sub-task	Days
Open the bitbox-testkit tracking issue (lift list from #548)	0.1
Review testkit PR	0.5
Action-pin bump PR in this repo	0.1
Total in this repo	0.7 days

The actual scenario implementation in bitbox-testkit is ~4-5 engineer-days (see #548 estimate breakdown). That's tracked there, not here.

Related

• Tier 2: extend BitBox02 firmware simulator beyond hardware_connect_bitbox #548 — Tier 2 simulator scope (defines the scenarios)
• DFXswiss/bitbox-testkit — where the scenarios live
• .github/workflows/bitbox-simulator.yml:72 — action-pin bump target