feat(manager-core,picloud): accept email on admin create + patch

The /admins create/patch endpoints now plumb email through to the
repo so the dashboard's invite + edit forms aren't silently dropping
it on the floor. Discovered during smoke testing — the database
column existed and was exposed in the response DTO, but neither
the request DTO nor the repo's create() accepted it.

CreateAdminRequest gains optional email; PatchAdminRequest gains
email with JSON Merge Patch semantics:
  absent     → don't change
  null       → clear (write NULL)
  "<string>" → set to that value

The tri-state needs Option<Option<String>> with a tiny custom
deserializer; serde collapses absent and null otherwise.

normalize_email() trims, treats blanks as None, and rejects
obviously bogus values (no '@', >254 chars) with a 422. Real
email verification is a future concern.

Repo trait gains an email parameter on create() and a new
update_email() method. The unique-violation branch in create now
inspects constraint() to distinguish duplicate username from
duplicate email.

Integration test exercises create-with-email, PATCH null clears,
PATCH value sets, PATCH without email key no-ops on email.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/picloud/tests/api.rs

@@ -36,7 +36,7 @@ async fn server_with_app(pool: PgPool) -> (TestServer, String) {
     let auth = picloud::AuthDeps::from_pool(pool.clone());
     let hash = hash_password("test-pw").expect("hash");
     auth.users
-        .create("test-admin", &hash, InstanceRole::Owner)
+        .create("test-admin", &hash, InstanceRole::Owner, None)
         .await
         .expect("seed admin");
 
@@ -114,6 +114,47 @@ async fn auth_me_returns_principal_with_role_and_email(pool: PgPool) {
     assert!(body["id"].as_str().is_some());
 }
 
+#[ignore = "needs DATABASE_URL pointing at a running Postgres"]
+#[sqlx::test(migrations = "../manager-core/migrations")]
+async fn create_admin_accepts_email_and_patch_clears_it(pool: PgPool) {
+    let s = server(pool).await;
+    // Create with email set.
+    let created = s
+        .post("/api/v1/admin/admins")
+        .json(&json!({
+            "username": "alice",
+            "password": "correct-horse-battery",
+            "instance_role": "member",
+            "email": "alice@example.com",
+        }))
+        .await;
+    created.assert_status(axum::http::StatusCode::CREATED);
+    let body: Value = created.json();
+    let alice_id = body["id"].as_str().expect("id").to_string();
+    assert_eq!(body["email"], "alice@example.com");
+
+    // Patch with email present-and-null clears it.
+    let cleared = s
+        .patch(&format!("/api/v1/admin/admins/{alice_id}"))
+        .json(&json!({ "email": null }))
+        .await;
+    cleared.assert_status_ok();
+    assert!(cleared.json::<Value>()["email"].is_null());
+
+    // Patch with email omitted is a no-op (doesn't clobber a re-set).
+    let reset = s
+        .patch(&format!("/api/v1/admin/admins/{alice_id}"))
+        .json(&json!({ "email": "alice2@example.com" }))
+        .await;
+    reset.assert_status_ok();
+    let omit = s
+        .patch(&format!("/api/v1/admin/admins/{alice_id}"))
+        .json(&json!({ "username": "alice" })) // no email key
+        .await;
+    omit.assert_status_ok();
+    assert_eq!(omit.json::<Value>()["email"], "alice2@example.com");
+}
+
 // ============================================================================
 // Script CRUD
 // ============================================================================