PipelineMerge, SchematicPublish, and GitOpsSync ceremony merkle
leaves are now the canonical_hash() of a GovernanceEnvelope,
binding git ref + governance metadata into a single auditable
32-byte hash.
Uses the resolution's resolved_at timestamp for deterministic
envelope construction.
Non-git ceremony types (MutationIntent, Custom) unchanged.
Signed-off-by: Tyler King <tking@guildhouse.dev>