internal/identity/spiffe.go: SpiffeURI format + MintSVID via step CLI;
internal/identity/spiffe_test.go: mock-transport tests with self-signed
SPIFFE URI SAN cert. Spike passes: step CLI supports --san with URI SANs.
Fallback to mTLS identity NOT needed.
---ci---
project: orca
phase: 01.5
milestone: v0.11
status: execute
---/ci---
Jon Chery