Rename express/ to backend/ and update references

Update paths in sync.sh, master/main.go, and CLAUDE.md to reflect
the directory rename.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/diachron/mgmt/add-user.ts

@@ -0,0 +1,69 @@
+// add-user.ts
+// Management command to create users from the command line
+
+import { hashPassword } from "../auth/password";
+import { PostgresAuthStore, pool } from "../database";
+
+async function main(): Promise<void> {
+    const args = process.argv.slice(2);
+
+    if (args.length < 2) {
+        console.error(
+            "Usage: ./mgmt add-user <email> <password> [--display-name <name>] [--active]",
+        );
+        process.exit(1);
+    }
+
+    const email = args[0];
+    const password = args[1];
+
+    // Parse optional flags
+    let displayName: string | undefined;
+    let makeActive = false;
+
+    for (let i = 2; i < args.length; i++) {
+        if (args[i] === "--display-name" && args[i + 1]) {
+            displayName = args[i + 1];
+            i++;
+        } else if (args[i] === "--active") {
+            makeActive = true;
+        }
+    }
+
+    try {
+        const store = new PostgresAuthStore();
+
+        // Check if user already exists
+        const existing = await store.getUserByEmail(email);
+        if (existing) {
+            console.error(`Error: User with email '${email}' already exists`);
+            process.exit(1);
+        }
+
+        // Hash password and create user
+        const passwordHash = await hashPassword(password);
+        const user = await store.createUser({
+            email,
+            passwordHash,
+            displayName,
+        });
+
+        // Optionally activate user immediately
+        if (makeActive) {
+            await store.updateUserEmailVerified(user.id);
+            console.log(
+                `Created and activated user: ${user.email} (${user.id})`,
+            );
+        } else {
+            console.log(`Created user: ${user.email} (${user.id})`);
+            console.log("  Status: pending (use --active to create as active)");
+        }
+    } finally {
+        await pool.end();
+    }
+}
+
+main().catch((err) => {
+    console.error("Failed to create user:", err.message);
+    process.exit(1);
+});