refactor: workspace secrets-core + secrets-mcp MCP SaaS

- Split library (db/crypto/service) and MCP/Web/OAuth binary
- Add deploy examples and CI/docs updates

Made-with: Cursor

crates/secrets-core/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "secrets-core"
+version = "0.1.0"
+edition.workspace = true
+
+[lib]
+name = "secrets_core"
+path = "src/lib.rs"
+
+[dependencies]
+aes-gcm.workspace = true
+anyhow.workspace = true
+chrono.workspace = true
+rand.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+serde_yaml.workspace = true
+sha2.workspace = true
+sqlx.workspace = true
+toml.workspace = true
+tokio.workspace = true
+tracing.workspace = true
+uuid.workspace = true
+
+[dev-dependencies]
+tempfile = "3"