test: add the Pubky marketplace wallet-leg journey

[ovitrif]

Parent: #712
Source: Pubky marketplace Bitkit team brief
Counterpart: synonymdev/bitkit-android#1212

Scope

• Cover watch-only seller claim, buyer contact/link prerequisite, incoming Payment Request presentation, approval, on-chain payment, and confirmation on regtest.
• Reuse shared accessibility identifiers and document required external fixtures.
• Run the journey against the current implementation first so it establishes the baseline and exposes remaining gaps.

Acceptance criteria

• The journey passes on a clean environment.
• Evidence is captured for each boundary in the wallet leg.