Promote the package to a single-member cargo workspace
First step toward the split in
`docs/plans/2026-05-08-workspace-split.md`. Layout is unchanged;
later commits will add `quire-lib` and `quire-ci` as members.

Assisted-by: Claude Opus 4.7 (1M context) via Claude Code
change sknoulzoxmxvwukqxktmzknryppuurpk
commit 164c99a38c3d4f0e5b78752b26cabdbdb354c454
author Alpha Chen <alpha@kejadlen.dev>
date
parent qovrotyy 
diff --git a/Cargo.toml b/Cargo.toml
index f38a8eb..99cacc8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,3 +1,7 @@
+[workspace]
+members = ["."]
+resolver = "3"
+
 [package]
 name = "quire"
 version = "0.1.0"