feat: accept allowance offers automatically on the allowee's wallet

[ovitrif]

Twin: synonymdev/bitkit-ios#807
Refs: #1340

Problem or use case

When the allower offers an allowance, the allowee has to tap Accept before it becomes active. The money and the decision are the allower's, so the tap only adds friction, and until the allowee opens Bitkit and accepts, nothing is paid automatically. @aldertnl raised this after the allowances demo.

Proposed solution

• When an incoming allowance proposal makes this wallet the allowee, meaning the proposer is the allower, Bitkit accepts it automatically through the SDK and posts a notification such as "{allower} set up an allowance for you". No review sheet opens.
• A proposal authored by the allowee, a payee asking for an allowance, still opens the review sheet with Accept and Decline on the allower's wallet.
• The allowee still sees the allowance in the list and can end it from its detail sheet.
• No SDK or protocol change: acceptance is an ordinary lifecycle message, and @Jasonvdb confirmed the protocol does not require the allowee's explicit consent.

Done when:

• An allower's offer becomes active on both wallets with no tap on the allowee's side, and the allowee is notified.
• An allowee's ask still waits for the allower's decision.
• The set-and-accept.xml journey reflects the automatic acceptance.

Alternatives considered

• Keep the review sheet for every offer, as the first implementation does. It follows the protocol's two-party shape but adds a step the allowee never needs to decide.
• A setting to choose between both. Not needed for a first version.

Additional context

• Ships as a PR stacked on the implementation in the refs above.