feat: initial playable npvz implementation

ncurses-based Plants vs. Zombies in the terminal.

- 5×9 grid, 5 waves of zombies
- Plants: 🌻 🫛 🪨 🍒 🧊 with sun economy
- Zombies: 🧟 🪖 🪣 with armor/body HP stages
- Projectiles (·), lawn mower 🚜, shovel 🪏
- Emoji-based rendering with ncursesw wide char support
- VFX: hit flash, death flash, 💥 cherry bomb
- Chiptune SFX via afplay (sine/square/sawtooth/noise synth)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>