[E5-1] `CO_BuyDedicatedSyncTraffic` wallet operation

[salindne]

New AmuletOperation constructor + handleBuyDedicatedSyncTraffic + COO_* outcome, exercising the dedicated buy choice.

Key files: daml/splice-wallet/daml/Splice/Wallet/Install.daml:258 (CO_BuyMemberTraffic), :297, :63-65, :161/189

Acceptance criteria:

• Wallet treasury can enqueue a dedicated-sync buy

Depends on: E1-3

Epic: #8

Source: docs/planning/extending-mainnet-work-plan.md