[VID-1343] Add CallState.e2ee_enabled

Advertise end-to-end encryption to clients in the SFU CallState (carried in
JoinResponse.call_state) so clients enable their frame encryptor. The large
models.pb.go diff is the regenerated rawDesc block; the only semantic change
is the new field + getter. Regenerated with the pinned toolchain (protoc
v3.21.5, protoc-gen-go v1.28.1).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Alessandro Toppi