Expose solver permission level (read / read-write) in the Add Solver UI

[mostronatorcoder]

Summary

When an operator adds a solver via Mostrix, the UI should let them choose the permission level (read-only or read-write) before submitting.

Context

Mostro node (PR #708 — merged) added two solver permission levels:

• read: solver can take disputes, receive context, and communicate with parties, but cannot execute admin-settle or admin-cancel
• read-write (default): full solver behavior including settle/cancel

The Mostro protocol spec for admin_add_solver already supports this via the payload format:

npub1...:read        -> read-only solver
npub1...:read-write  -> read-write solver (default)

The feature is live in the Mostro node. The only way to set a read-only solver today is to manually append :read to the npub in the order message payload — the Mostrix admin UI does not expose this choice.

Current UX problem

An operator using Mostrix to add a solver has no way to select the permission level through the UI. They must either:

1. Know to append :read to the npub in the raw order message, or
2. Default to read-write even when they only want to register a read-only solver (like Serbero)

This creates friction and risk: operators may unintentionally grant write permissions to agents (e.g. Serbero) that should never move funds.

Proposed change

In the Mostrix admin panel's Add Solver screen, add a permission level selector (radio buttons or dropdown) before the submit action:

• Read-write (default, backwards-compatible)
• Read-only

When the operator submits, Mostrix should construct the admin-add-solver order with the appropriate permission suffix in the payload (npub:read or npub:read-write), matching the protocol spec.

Expected behavior

Operator selects	Payload sent to Mostro
Read-only	{"text_message": "npub...:read"}
Read-write	{"text_message": "npub...:read-write"}

Motivation

This enables clean separation:

• AI agents (e.g. Serbero) registered as read-only solvers: they assist in dispute resolution but cannot move funds under any circumstances
• Human solvers registered as read-write: retain full dispute resolution authority

Security is enforced at the Mostro node level, not by relying on agent behavior.

References

• Mostro PR #708 — solver permission levels implementation
• Mostro issue #707 — original feature request
• Mostro protocol spec: admin_add_solver
• Serbero README — Serbero registers as read-only solver for Phase 3 mediation