New plugin hook op: $.tool.check lets a plugin test a tool call without running it

Plugins (add-on scripts that can hook into Claude Code's behavior) can now call a new $.tool.check operation. Given a tool name and its input, this runs the same permission and argument checks Claude Code would normally run before executing that tool, and returns the verdict (allowed, denied, etc.) without actually running the tool. It's also wired into the tool-call hook used by the Claude Code SDK, which now validates the tool name and input before dispatching to this new check.