Add JoinRpg as a new web provider integration

JoinRpg.ru exposes a standards-compliant OpenID Connect authorization
server at id.joinrpg.ru (OpenIddict-based), so only the issuer needs to
be configured; discovery, PKCE and standard userinfo claim names are
all supported out of the box.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X8qhsMdzNDU1YbSRm56Z4E

src/OpenIddict.Client.WebIntegration/OpenIddictClientWebIntegrationProviders.xml

@@ -1251,6 +1251,28 @@
     </Environment>
   </Provider>
 
+  <!--
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+  -->
+
+  <Provider Name="JoinRpg" Id="698f413f-21e1-4be1-9b7f-c96f91bbf41d"
+            Documentation="https://github.com/joinrpg/joinrpg-net/blob/master/docs/adr004-oauth-server.md">
+    <!--
+      Note: the "email", "phone" and "profile" scopes are not strictly required but are requested
+      by default to receive the corresponding standard claims from the userinfo endpoint.
+    -->
+
+    <Environment Issuer="https://id.joinrpg.ru/">
+      <Scope Name="email" Default="true" Required="false" />
+      <Scope Name="phone" Default="true" Required="false" />
+      <Scope Name="profile" Default="true" Required="false" />
+    </Environment>
+  </Provider>
+
   <!--
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