buoy-2026.06.19

change: update README roadmap and add optional chaining example

• new: add optional chaining code example demonstrating nil-safe member access syntax
• change: revise roadmap "Now" milestone to reflect shipped features (OOP, generics, async/await, optional chaining, file I/O, date/time)
• change: reorganize roadmap "Next" milestone to include .buipkg packaging and visual layout editor
• change: remove .buipkg from "Now" and debugger features from "Later" to better reflect current state