feat(config): persist database URL to ~/.config/secrets/config.toml

- Add 'secrets config set-db/show/path' subcommands
- Remove dotenvy and DATABASE_URL env var support
- Config file created with 0600 permission
- Bump version to 0.3.0

Made-with: Cursor

src/commands/mod.rs

@@ -1,4 +1,5 @@
 pub mod add;
+pub mod config;
 pub mod delete;
 pub mod search;
 pub mod update;