cli: add 'completions <SHELL>' subcommand via clap_complete

crates/relicario-cli/tests/smart_inputs.rs

@@ -0,0 +1,30 @@
+use assert_cmd::Command;
+use predicates::str::contains;
+
+#[test]
+fn completions_bash_emits_script() {
+    Command::cargo_bin("relicario").unwrap()
+        .args(["completions", "bash"])
+        .assert()
+        .success()
+        .stdout(contains("_relicario"))
+        .stdout(contains("complete -F"));
+}
+
+#[test]
+fn completions_zsh_emits_script() {
+    Command::cargo_bin("relicario").unwrap()
+        .args(["completions", "zsh"])
+        .assert()
+        .success()
+        .stdout(contains("#compdef relicario"));
+}
+
+#[test]
+fn completions_fish_emits_script() {
+    Command::cargo_bin("relicario").unwrap()
+        .args(["completions", "fish"])
+        .assert()
+        .success()
+        .stdout(contains("complete -c relicario"));
+}