Adds Cloud Signature Consortium (CSC) integration for AES/QES signing
against a configured TSP. v1 ships as instance-wide configuration via
environment variables, with per-envelope signature level selection,
license gating, and an OAuth-driven signing flow (capture + FIFO
signers, SAD session, blocking/in-progress recipient pages).
Includes signature level compatibility checks (role, signing order,
dictate next signer), envelope mutability assertions, Prisma migration
for signature level and CSC tables, and docs for the new signing
certificate options.
Lucas Smith