P0.3: Scaffold miroir-proxy crate
- Added Cargo.toml with axum, tokio, reqwest, serde, tracing, prometheus
- Created main.rs: binds :7700 (main API) and :9090 (metrics)
- Route handler stubs: documents, search, indexes, settings, tasks, health, admin
- auth.rs: bearer-token dispatch skeleton (client/admin token kinds)
- middleware.rs: tracing/logging + Prometheus middleware stubs
- Fixed miroir-core/migration.rs: Display impls, Instant serialization, borrow fixes
Acceptance:
- Binary builds successfully
- Health endpoint returns {"status":"available"}
- Stripped binary: 2.3 MB (< 20 MB target)
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>