refactor: extract omnigraph-config crate from omnigraph-server

Move config.rs (schema + loader + resolvers) into a new clean-leaf crate
(serde/serde_yaml/clap/color-eyre). The server aliases it via
`pub use omnigraph_config as config;` so every internal `config::` path and
the `pub use config::{...}` re-exports resolve unchanged. No behavior change;
the 12 config tests move verbatim and pass. First step of RFC-002 V0.

crates/omnigraph-config/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "omnigraph-config"
+version = "0.6.1"
+edition = "2024"
+description = "Configuration schema and loader for the Omnigraph graph database."
+license = "MIT"
+repository = "https://github.com/ModernRelay/omnigraph"
+homepage = "https://github.com/ModernRelay/omnigraph"
+documentation = "https://docs.rs/omnigraph-config"
+
+[dependencies]
+serde = { workspace = true }
+serde_yaml = { workspace = true }
+clap = { workspace = true }
+color-eyre = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }

crates/omnigraph-server/Cargo.toml

@@ -22,6 +22,7 @@ aws = ["dep:aws-config", "dep:aws-sdk-secretsmanager"]
 omnigraph = { package = "omnigraph-engine", path = "../omnigraph", version = "0.6.1" }
 omnigraph-compiler = { path = "../omnigraph-compiler", version = "0.6.1" }
 omnigraph-policy = { path = "../omnigraph-policy", version = "0.6.1" }
+omnigraph-config = { path = "../omnigraph-config", version = "0.6.1" }
 axum = { workspace = true }
 clap = { workspace = true }
 color-eyre = { workspace = true }

crates/omnigraph-server/src/lib.rs

@@ -1,6 +1,6 @@
 pub mod api;
 pub mod auth;
-pub mod config;
+pub use omnigraph_config as config;
 pub mod graph_id;
 pub mod identity;
 pub mod policy;