fix(worker): make external MCP filter params optional, surface tool errors

Nullable filter/patch params across the External/ MCP tool classes (ListTasks,
UpdateTask, AddSubtask, ReviewTask, SetMyDay, SetListConfig/SetTaskConfig,
CreateList/UpdateList) lacked C# default values, so the generated tool schema
marked them required — MCP clients omitting them (the common case) failed.
Gave every such parameter a default value.

Also registered a call-tool filter (ExternalMcpExceptionFilter) on the external
MCP host that translates InvalidOperationException/ArgumentException into
McpException, since the SDK's own catch-all discards ex.Message for any other
exception type and returns a generic "An error occurred invoking 'X'." string.

Added a reflection-based schema test sweeping every [McpServerToolType] class
to guard against reintroducing a required-but-nullable parameter.

src/ClaudeDo.Worker/External/ExternalMcpService.cs

@@ -107,9 +107,9 @@ public sealed class ExternalMcpService
         "Valid status values: Idle, Queued, Running, WaitingForReview, WaitingForChildren, Done, Failed, Cancelled.")]
     public async Task<IReadOnlyList<TaskDto>> ListTasks(
         string listId,
-        string? createdBy,
-        string? status,
-        CancellationToken cancellationToken)
+        string? createdBy = null,
+        string? status = null,
+        CancellationToken cancellationToken = default)
     {
         TaskStatus? statusFilter = null;
         if (!string.IsNullOrWhiteSpace(status))
@@ -193,10 +193,10 @@ public sealed class ExternalMcpService
     [McpServerTool, Description("Update an existing task's title, description, and/or commit type. Pass null to leave a field unchanged. Refuses if the task is currently Running.")]
     public async Task<TaskDto> UpdateTask(
         string taskId,
-        string? title,
-        string? description,
-        string? commitType,
-        CancellationToken cancellationToken)
+        string? title = null,
+        string? description = null,
+        string? commitType = null,
+        CancellationToken cancellationToken = default)
     {
         var task = await _tasks.GetByIdAsync(taskId, cancellationToken)
             ?? throw new InvalidOperationException($"Task {taskId} not found.");
@@ -219,8 +219,8 @@ public sealed class ExternalMcpService
     public async Task<TaskDto> AddSubtask(
         string taskId,
         string title,
-        int? orderNum,
-        CancellationToken cancellationToken)
+        int? orderNum = null,
+        CancellationToken cancellationToken = default)
     {
         if (string.IsNullOrWhiteSpace(title))
             throw new InvalidOperationException("title is required.");
@@ -300,8 +300,8 @@ public sealed class ExternalMcpService
     public async Task<TaskDto> ReviewTask(
         string taskId,
         string decision,
-        string? feedback,
-        CancellationToken cancellationToken)
+        string? feedback = null,
+        CancellationToken cancellationToken = default)
     {
         _ = await _tasks.GetByIdAsync(taskId, cancellationToken)
             ?? throw new InvalidOperationException($"Task {taskId} not found.");
@@ -619,8 +619,8 @@ public sealed class ExternalMcpService
     public async Task<TaskDto> SetMyDay(
         string taskId,
         bool isMyDay,
-        int? sortOrder,
-        CancellationToken cancellationToken)
+        int? sortOrder = null,
+        CancellationToken cancellationToken = default)
     {
         await using var ctx = await _dbFactory.CreateDbContextAsync(cancellationToken);