✨➖📝 cli, vanth, meta, flake: Simplify dependencies, add meta crate, and improve docs

- Removed dependencies `sqlx` and `bevy_app` to simplify the project.
- Added new crate `vanth_meta` for generating example SVGs.
- Updated CLI tests to use `assert_cmd` for better test assertions.
- Enhanced README with comprehensive library and CLI usage documentation.
- Modified `Store::write` in `vanth` crate to return the content hash.
- Set `checkPhase` to empty in Nix flake configuration.

crates/meta/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "vanth_meta"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]