chore: align owner DID terminology

[skgbafa]

Summary

• rename encryption network protocol and route fields from principal terminology to ownerDid
• keep the existing database column mapped for compatibility while exposing ownerDid in Rust/JSON surfaces
• update authorization checks and tests to use owner terminology

Validation

• cargo test -p tinycloud-core encryption_network
• cargo check -p tinycloud-node
• git diff --check