Add channel search and subscription

server/QMax.Api/Infrastructure/Max/IMaxBridgeClient.cs

@@ -19,4 +19,13 @@ public interface IMaxBridgeClient
     Task<MaxActionResult> SetReactionAsync(string externalChatId, string externalMessageId, string? currentText, string emoji, CancellationToken cancellationToken);
     Task<MaxActionResult> ClearReactionAsync(string externalChatId, string externalMessageId, string? currentText, string emoji, CancellationToken cancellationToken);
     Task<MaxMediaDownload?> DownloadMediaAsync(string remoteUrl, CancellationToken cancellationToken);
+    Task<IReadOnlyList<MaxChannelSearchResult>> SearchChannelsAsync(string query, CancellationToken cancellationToken)
+    {
+        return Task.FromResult<IReadOnlyList<MaxChannelSearchResult>>(Array.Empty<MaxChannelSearchResult>());
+    }
+
+    Task<MaxChatUpdate?> JoinChannelAsync(string link, CancellationToken cancellationToken)
+    {
+        return Task.FromResult<MaxChatUpdate?>(null);
+    }
 }

server/QMax.Api/Infrastructure/Max/MaxBridgeModels.cs

@@ -65,3 +65,11 @@ public sealed record MaxChatPresence(
     bool IsTyping,
     string? StatusText,
     DateTimeOffset UpdatedAt);
+
+public sealed record MaxChannelSearchResult(
+    string ExternalId,
+    string Title,
+    string? AvatarUrl,
+    string? ChatUrl,
+    bool IsSubscribed,
+    string? Description = null);

server/QMax.Api/Infrastructure/Max/MockMaxBridgeClient.cs

@@ -108,6 +108,30 @@ public sealed class MockMaxBridgeClient : IMaxBridgeClient
         return Task.FromResult<MaxMediaDownload?>(null);
     }
 
+    public Task<IReadOnlyList<MaxChannelSearchResult>> SearchChannelsAsync(string query, CancellationToken cancellationToken)
+    {
+        IReadOnlyList<MaxChannelSearchResult> result = string.IsNullOrWhiteSpace(query)
+            ? []
+            : [new MaxChannelSearchResult("mock-channel", "Mock channel", null, "mock-channel", false, "Mock MAX channel")];
+        return Task.FromResult(result);
+    }
+
+    public Task<MaxChatUpdate?> JoinChannelAsync(string link, CancellationToken cancellationToken)
+    {
+        return Task.FromResult<MaxChatUpdate?>(new MaxChatUpdate(
+            "mock-channel",
+            "Mock channel",
+            null,
+            DateTimeOffset.UtcNow,
+            [],
+            "Mock channel subscribed",
+            false,
+            DateTimeOffset.UtcNow,
+            null,
+            MockChatUrl("mock-channel"),
+            "Channel"));
+    }
+
     private static string MockChatUrl(string externalChatId)
     {
         return $"pymax://mock/{Uri.EscapeDataString(externalChatId)}";

server/QMax.Api/Infrastructure/Max/WorkerMaxBridgeClient.cs

@@ -160,6 +160,25 @@ public sealed class WorkerMaxBridgeClient(
         }
     }
 
+    public async Task<IReadOnlyList<MaxChannelSearchResult>> SearchChannelsAsync(string query, CancellationToken cancellationToken)
+    {
+        return await SendAsync<IReadOnlyList<MaxChannelSearchResult>>(
+                HttpMethod.Post,
+                "/channels/search",
+                new { query },
+                cancellationToken)
+            ?? Array.Empty<MaxChannelSearchResult>();
+    }
+
+    public async Task<MaxChatUpdate?> JoinChannelAsync(string link, CancellationToken cancellationToken)
+    {
+        return await SendAsync<MaxChatUpdate>(
+            HttpMethod.Post,
+            "/channels/join",
+            new { link },
+            cancellationToken);
+    }
+
     private async Task<T?> SendAsync<T>(HttpMethod method, string path, object? body, CancellationToken cancellationToken)
     {
         try