feat(discord): enable session join leave buttons

Move neutral join/leave handlers into GmRelay.Shared so Telegram and Discord share capacity, waitlist, duplicate-click, and schedule-update behavior.

Add Discord component routing for join_session and leave_session buttons with deferred ephemeral replies and serialized schedule message updates.

Bump version to 2.5.0 and update Discord docs.

Refs #29

src/GmRelay.Web/Components/Layout/NavMenu.razor

@@ -56,7 +56,7 @@
                     </button>
                 </form>
 
-                <div class="nav-version">v2.4.0</div>
+                <div class="nav-version">v2.5.0</div>
             </div>
         </Authorized>
         <NotAuthorized>

src/GmRelay.Web/packages.lock.json

@@ -243,7 +243,11 @@
         }
       },
       "gmrelay.shared": {
-        "type": "Project"
+        "type": "Project",
+        "dependencies": {
+          "Dapper": "[2.1.72, )",
+          "Npgsql": "[10.0.2, )"
+        }
       }
     }
   }