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/views/gitea_integration/admin/settings/show.html.erb

@@ -0,0 +1,41 @@
+<%#-- 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.
+++#%>
+<% html_title t(:label_administration), t(:label_gitea_integration), t(:label_setting_plural) %>
+
+<%= render(GiteaIntegration::Admin::PageHeaderComponent.new) %>
+
+<%= settings_primer_form_with(url: gitea_integration_admin_settings_path, method: :patch) do |f| %>
+  <% if @webhook_secret.blank? %>
+    <%= render(Primer::Alpha::Banner.new(scheme: :warning, icon: :alert, mb: 4)) do %>
+      <%= t(:text_gitea_webhook_secret_missing_warning) %>
+    <% end %>
+  <% end %>
+  <%= render GiteaIntegration::Admin::SettingsForm.new(f,
+                                                       comment_user: @gitea_comment_user,
+                                                       webhook_secret: @webhook_secret) %>
+<% end %>