style: capitalize "Relicario" in prose / UI / CLI help

Brand name uses capital R in user-facing text — extension UI strings,
CLI clap help / descriptions / error prose, markdown docs. Lowercase
preserved for the binary command, crate names, npm package, file
paths, env vars, and code identifiers.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/relicario-cli/tests/backup.rs

@@ -66,7 +66,7 @@ fn restore_refuses_non_empty_target() {
         .unwrap();
     assert!(!out.status.success());
     let err = String::from_utf8(out.stderr).unwrap();
-    assert!(err.contains("already contains a relicario vault"), "stderr: {err}");
+    assert!(err.contains("already contains a Relicario vault"), "stderr: {err}");
 }
 
 #[test]