✨➖📝 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/cli/Cargo.toml

@@ -2,6 +2,11 @@
 name = "vanth_cli"
 version.workspace = true
 edition.workspace = true
+default-run = "vanth"
+
+[[bin]]
+name = "vanth"
+path = "src/main.rs"
 
 [dependencies]
 clap.workspace = true
@@ -10,6 +15,7 @@ serde_json.workspace = true
 vanth = { path = "../vanth" }
 tracing.workspace = true
 tracing-subscriber.workspace = true
+assert_cmd.workspace = true
 
 [dev-dependencies]
 tempfile = { workspace = true }