feat: reject pegin flow

[asoto-iov]

Adds a new reject-pegin path so a member can explicitly reject a pegin request and close the corresponding pegin flow when the on-chain RejectPeginRegistered event is observed.

• coordinator: new RejectPeginFlow and RejectPeginProcessor, plus pegin-flow integration that transitions to Done with a Rejected completion outcome on confirmed RejectPeginRegistered.
• user-api: new POST /member/reject-pegin endpoint.
• transaction-dispatcher: new rejectPegin interaction on PeginManager.
• cli: cli-operations.sh user reject-pegin command.
• config: [flows.reject_pegin] section with min_tx_confirmations and blocks_delay_for_tx_check.

Description

Motivation and Context

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (code improvement without changing existing functionality)

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[Copilot]

Pull request overview

Adds a new “reject pegin” user/member workflow end-to-end (CLI → user-api → coordinator flow → transaction-dispatcher contract call), and wires coordinator pegin flows to close as Rejected when the on-chain RejectPeginRegistered event is confirmed.

Changes:

• Introduces RejectPeginFlow/RejectPeginProcessor and persists them via the coordinator store.
• Adds POST /member/reject-pegin to user-api and a corresponding CLI command.
• Adds transaction-dispatcher support for PeginManager.rejectPegin, plus event decoding/handling to close pegin flows as rejected.

Reviewed changes

Copilot reviewed 29 out of 30 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
user-api/src/server.rs	Adds /member/reject-pegin endpoint and request payload type.
user-api/Cargo.toml	Adds bitcoin dependency for Txid.
transaction-dispatcher/src/types.rs	Adds RejectPeginInput/Output aliases.
transaction-dispatcher/src/rsk_gateway.rs	Adds reject_pegin gateway API + wiring to new invoke.
transaction-dispatcher/src/contracts/pegin_manager.rs	Exposes RejectPeginInvoke + contract method wrapper.
transaction-dispatcher/src/contracts/interactions/reject_pegin.rs	Implements RejectPeginInvoke interaction.
transaction-dispatcher/src/contracts/interactions/mod.rs	Registers reject_pegin interaction module.
coordinator/src/user_requests.rs	Adds RejectPeginRequest + serialization/deserialization tests.
coordinator/src/types.rs	Adds RejectPeginRegistered event decoding and user request variant.
coordinator/src/store.rs	Adds store keys/prefixes for reject-pegin flows.
coordinator/src/main.rs	Passes reject-pegin flow config into Coordinator::new.
coordinator/src/flows/reject_pegin/reject_pegin_processor.rs	New processor to drive reject-pegin flow and confirm RSK events.
coordinator/src/flows/reject_pegin/reject_pegin_flow.rs	New state machine for reject-pegin BitVMX + RSK registration.
coordinator/src/flows/reject_pegin/mod.rs	Exposes reject-pegin flow/processor module API.
coordinator/src/flows/pegin/pegin_processor.rs	Handles RejectPeginRegistered to close active pegin flows.
coordinator/src/flows/pegin/pegin_flow.rs	Adds rejected completion outcome and transitions to Done on rejection.
coordinator/src/flows/mod.rs	Registers reject_pegin module.
coordinator/src/flows/funding_info_flow.rs	Explicitly ignores UserRequests::RejectPegin.
coordinator/src/flows/common/context.rs	Adds clippy allow for GlobalContext field naming lint.
coordinator/src/flows/committee/setup_committee_processor.rs	Explicitly ignores UserRequests::RejectPegin.
coordinator/src/coordinator.rs	Wires RejectPeginProcessor into coordinator processor set + mocks.
coordinator/src/config.rs	Adds [flows.reject_pegin] config section and defaults.
config/base.toml	Adds [flows.reject_pegin] defaults in base configuration.
common/src/types.rs	Adds serde helpers for decimal-string CommitteeId and 0x-optional Txid.
common/src/msg_broker/bitvmx_types.rs	Adds BitVMX constants and RejectPeginData payload type.
cli/README.md	Documents new reject-pegin CLI usage and module file.
cli/operations/src/reject_pegin.rs	Implements CLI operation calling /member/reject-pegin with validation.
cli/operations/src/main.rs	Adds user reject-pegin CLI subcommand wiring.
cli-operations.sh	Documents the new user reject-pegin usage.
Cargo.lock	Records dependency graph changes from added bitcoin dependency.

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[fedejinich]

I think there might be a small race: RejectPeginRegistered is accepted from any non-Done pegin step, but bitvmx_protocol_id is only set after the flow processes PeginRequested. If the reject event is processed before that local step, the flow transitions to Done with bitvmx_protocol_id = None, and write_completion_marker() fails. The "risk" is that the rejected pegin does not close cleanly and may require intervention, restart, or admin cleanup. Do you think this case is worth covering, or can we be more relaxed since this is not a productive feature? If so, we should either delay the reject event until PeginRequested has been applied, or reject this transition until the protocol id exists.