M1 foundation: fix proxy, pool HTTP clients, split services, add ApiError + RLS

- Fix proxy body forwarding, round-robin load balancing, response streaming
- Pool reqwest::Client in proxy, control, and gateway (no per-request alloc)
- Harden CORS in gateway/main.rs (was allow_origin(Any), now uses ALLOWED_ORIGINS)
- Add common/src/error.rs: ApiError type with structured JSON responses
- Add common/src/rls.rs: RlsTransaction extractor for deduplicated RLS setup
- Fix tracing in all standalone binaries (EnvFilter instead of unused var)
- Dockerfile multi-stage: separate worker-runtime, control-runtime, proxy-runtime targets
- docker-compose.yml: split into worker/system/proxy services with health checks
- Fix Grafana port mapping in pillar-system (3030:3000)
- Add config/prometheus.yml and config/vmagent.yml
- Add .env.example with all required variables
- 55 tests pass (49 run + 6 ignored integration tests requiring external services)

Made-with: Cursor

common/src/lib.rs

@@ -1,6 +1,8 @@
 pub mod cache;
 pub mod config;
 pub mod db;
+pub mod error;
+pub mod rls;
 
 pub use cache::{CacheLayer, CacheError, CacheResult};
 pub use config::{Config, ProjectContext};