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/src/lib.rs

@@ -0,0 +1,6 @@
+pub mod audit;
+pub mod config;
+pub mod crypto;
+pub mod db;
+pub mod models;
+pub mod service;