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/ConfigMcpTools.cs

@@ -31,7 +31,8 @@ public sealed class ConfigMcpTools
 
     [McpServerTool, Description("Set a list's default model/system prompt/agent path/max turns. Passing all four as null clears the list config.")]
     public async Task SetListConfig(
-        string listId, string? model, string? systemPrompt, string? agentPath, int? maxTurns, CancellationToken cancellationToken)
+        string listId, string? model = null, string? systemPrompt = null, string? agentPath = null,
+        int? maxTurns = null, CancellationToken cancellationToken = default)
     {
         _ = await _lists.GetByIdAsync(listId, cancellationToken)
             ?? throw new InvalidOperationException($"List {listId} not found.");
@@ -53,7 +54,8 @@ public sealed class ConfigMcpTools
 
     [McpServerTool, Description("Set per-task config overrides (model/system prompt/agent path/max turns). Pass null for any field to clear that override.")]
     public async Task SetTaskConfig(
-        string taskId, string? model, string? systemPrompt, string? agentPath, int? maxTurns, CancellationToken cancellationToken)
+        string taskId, string? model = null, string? systemPrompt = null, string? agentPath = null,
+        int? maxTurns = null, CancellationToken cancellationToken = default)
     {
         _ = await _tasks.GetByIdAsync(taskId, cancellationToken)
             ?? throw new InvalidOperationException($"Task {taskId} not found.");