feat(api): Dockerfile for gRPC API crate

[Depo-dev]

Summary

No Dockerfile exists for the gRPC API crate. The production docker-compose.yml references a build at crates/api.

Acceptance Criteria

• Multi-stage Dockerfile: builder (rust:1.78-slim) + runtime (debian:bookworm-slim)
• Builder: cargo build --release -p trident-api
• Runtime: copy binary only
• Exposes port 50051 (gRPC)
• Final image < 100 MB
• docker build succeeds locally and in CI

Files

crates/api/Dockerfile (new)