GUI-key captcha verification

KeyVerify — Join Verification / Anti-Bot GUI
Stop scripted bots and mass-join attacks before they ever touch your world.
KeyVerify greets every joining player with a simple visual challenge: find
the one item in a grid of 15 that matches the code shown at the top. Real
players solve it in a second. Bots that auto-click, auto-move, or replay a
fixed sequence of packets get it wrong — and are kicked instantly, with a
clear warning logged to console so you can see exactly who's being screened
out.
No external dependencies. No NMS. No reflection. Pure Bukkit API, built for
long-term compatibility from 1.16.5 all the way through 1.21.x.
---
✨ Features
Automatic on join — the verification GUI opens the instant a player
connects, before they can move, break blocks, or take damage.
Randomized every time — a fresh 5-character code and a freshly
shuffled layout of 15 key items are generated per player, per join. There
is no fixed pattern to script against.
Instant bot detection — clicking any wrong key kicks the player
immediately and logs:
```
[KeyVerify] <PlayerName> might be a bot!
```
so you can watch your console (or pipe it into your log-monitoring setup)
and spot bot waves in real time.
Can't dodge it — closing the GUI without answering re-opens it
automatically; doing nothing for too long triggers a configurable timeout
kick.
Full freeze while unverified — movement, block breaking/placing,
interaction, and damage are all cancelled until the player passes (each
toggle configurable, or disable freezing entirely).
Fully configurable — GUI title, item materials, timeout length, and
every message are editable in `config.yml`, with color code support
(`&a`, `&c`, etc.).
Lightweight — one listener, no scheduler spam, no per-tick loops. Zero
measurable impact on TPS.
No player data collection. KeyVerify only tracks verification state
in memory for the duration of the join challenge; nothing is written to
disk about players.