fix: fix nil pointer dereference in ReportTask (#19045)

This pull request addresses a bug related to a nil pointer dereference
in the task reporting functionality.

### Bug Fixes and Error Handling:

* Updated `RegisterTools` in `mcp.go` to skip registering the
`ReportTask` tool in the remote MCP context when a task reporter is not
configured, preventing potential nil pointer dereference panics.
* Added a check in `toolsdk.go` to ensure task reporting dependencies
are available before invoking the reporter, returning an appropriate
error if not.

### Test Coverage:

* Added `TestReportTaskNilPointerDeref` in `toolsdk_test.go` to verify
that the system does not panic when task reporting dependencies are
missing and instead returns a clear error message.
* Added `TestReportTaskWithReporter` in `toolsdk_test.go` to validate
correct behavior when a task reporter is configured, ensuring the
handler processes the request as expected.

Signed-off-by: Thomas Kosiewski <tk@coder.com>

coderd/mcp/mcp.go

@@ -79,11 +79,15 @@ func (s *Server) RegisterTools(client *codersdk.Client) error {
 		return xerrors.Errorf("failed to initialize tool dependencies: %w", err)
 	}
 
-	// Register all available tools
+	// Register all available tools, but exclude tools that require dependencies not available in the
+	// remote MCP context
 	for _, tool := range toolsdk.All {
+		if tool.Name == toolsdk.ToolNameReportTask {
+			continue
+		}
+
 		s.mcpServer.AddTools(mcpFromSDK(tool, toolDeps))
 	}
-
 	return nil
 }