Add OpenProject Gitea integration plugin

Implements a Gitea integration for OpenProject following the same
patterns as the bundled GitHub and GitLab integrations.

- Webhook endpoint at /webhooks/gitea with HMAC-SHA256 verification
- Handles pull_request and issue_comment events
- Links Gitea PRs to work packages via OP# references or URLs
- Posts journal comments on WPs for PR lifecycle events
- Gitea tab on the work package split view
- V3 API endpoint: GET /api/v3/work_packages/:id/gitea_pull_requests
- Admin settings UI for bot user and webhook secret
- Nightly cron job to clean up unlinked PR records

app/forms/gitea_integration/admin/settings_form.rb

@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module GiteaIntegration
+  module Admin
+    class SettingsForm < ApplicationForm
+      form do |f|
+        f.autocompleter(
+          name: :gitea_user_id,
+          label: I18n.t(:label_gitea_actor),
+          caption: I18n.t(:text_gitea_actor_info),
+          autocomplete_options: {
+            component: "opce-user-autocompleter",
+            allowEmpty: true,
+            defaultData: false,
+            model: @comment_user_model
+          }
+        )
+
+        f.text_field(
+          name: :webhook_secret,
+          label: I18n.t(:label_gitea_webhook_secret),
+          caption: I18n.t(:text_gitea_webhook_secret_info),
+          value: @webhook_secret,
+          input_width: :xxlarge
+        )
+
+        f.submit(
+          name: :submit,
+          label: I18n.t(:button_save),
+          scheme: :primary
+        )
+      end
+
+      def initialize(comment_user: nil, webhook_secret: nil)
+        super()
+        @comment_user_model = comment_user.present? ? { id: comment_user.id, name: comment_user.name } : nil
+        @webhook_secret = webhook_secret
+      end
+    end
+  end
+end