Add local signer backup recovery flow

[ihordiachenko]

Adds opt-in local VLS signer backups with CLI inspection/conversion tooling. There are two available backup strategies:

• new-channels-only: default, low I/O, snapshots when a channel first becomes recoverable.
• periodic: snapshots new recoverable channels and then refreshes after configured recoverable-channel updates, with more disk writes

Backups can be created through:

 glcli signer run --backup-path, inspected with inspect-backup

Backups can be converted to CLN recoverchannel input with:

glcli signer convert-backup --format cln --path <backup file>

Tradeoffs

• Backups are best-effort during signer operation: write failures are logged and do not interrupt signing. The backup file is created only after a snapshot trigger, not immediately at startup.
• Peer addresses are stored from Greenlight’s peerlist alongside VLS state to close the main recovery-data gap.
• Only v1 channels supported for now