✨➖📝 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/tests/integration/main.rs

@@ -1,6 +1,6 @@
+use assert_cmd::Command;
 use std::io::Write;
 use std::path::Path;
-use std::process::Command;
 
 use serde::{Deserialize, Serialize};
 use serde_json::{Value, json};
@@ -8,33 +8,14 @@ use tempfile::tempdir;
 use vanth::{ContentHash, Vanth, hash as vanth_hash};
 
 fn run_vanth(args: &[&str], input: Option<&str>) -> (String, String, i32) {
-    let mut cmd = Command::new(env!("CARGO_BIN_EXE_vanth_cli"));
-    cmd.args(args);
-    if let Some(inp) = input {
-        let mut child = cmd
-            .stdin(std::process::Stdio::piped())
-            .stdout(std::process::Stdio::piped())
-            .stderr(std::process::Stdio::piped())
-            .spawn()
-            .unwrap();
-        {
-            let stdin = child.stdin.as_mut().unwrap();
-            stdin.write_all(inp.as_bytes()).unwrap();
-        }
-        let output = child.wait_with_output().unwrap();
-        (
-            String::from_utf8(output.stdout).unwrap(),
-            String::from_utf8(output.stderr).unwrap(),
-            output.status.code().unwrap(),
-        )
-    } else {
-        let output = cmd.output().unwrap();
-        (
-            String::from_utf8(output.stdout).unwrap(),
-            String::from_utf8(output.stderr).unwrap(),
-            output.status.code().unwrap(),
-        )
-    }
+    let mut cmd = Command::cargo_bin("vanth").unwrap();
+    let output = cmd.args(args).write_stdin(input.unwrap_or("")).output().unwrap();
+
+    (
+        String::from_utf8(output.stdout).unwrap(),
+        String::from_utf8(output.stderr).unwrap(),
+        output.status.code().unwrap(),
+    )
 }
 
 #[derive(Clone, Debug, Deserialize, PartialEq, Serialize, Vanth)]
@@ -72,7 +53,7 @@ fn test_write_get() {
         panic!("{}", stderr);
     }
     let hash = stdout.trim();
-    println!("x{}x", hash);
+    println!("{}", hash);
 
     let (stdout, stderr, exit) = run_vanth(&["get", "--db", &db_path, "--ty", &Foo::ty().to_string(), &hash], None);
     if exit != 0 {