Durability Alerts

# Durability Alerts 1.5.0

**Minecraft 1.21.6 – 1.21.8 only.** Older builds declared no upper version limit and
would crash on 1.21.9+. This one refuses to load there instead. A separate build for
1.21.9 – 1.21.11 is on the way.

## ⚡ New Features
- Armor and offhand are now watched, not just the main hand
- New corner HUD showing what is about to break, with a durability bar
- Alerts are now drawn by the mod: configurable size, position, duration and a dark backdrop
- "Test alert" button to calibrate the look without breaking a tool
- Sound picker with 26 named sounds and instant preview
- Any Minecraft sound ID now works: `minecraft:block.bell.use`
- Formatting menu for alert messages, each option shown in its own style
- Live preview of the message with colors applied
- Alerts can be edited instead of deleted and recreated
- Full Spanish translation

### Improvements
- Threshold detection rewritten: alerts arm when the item is above them and disarm when they fire
- Checks every tick instead of every five, so fast tools no longer skip the last-hits window
- AutoSwitch now prefers a healthy tool over an empty slot
- Alert list shows the sound, and the whole panel is centred
- Settings split into two columns with a manual language override
- `/durability` is the new command, `/golpes` still works as an alias

### Fixes
- **AutoSwitch was never saved** and reset to off on every restart
- Alerts firing when swapping between two tools of the same type
- Alerts not firing at the exact threshold after a tool swap
- A corrupt config was overwritten silently; it is now backed up before defaults are written
- Config is read and written as UTF-8, so accented characters and symbols survive
- `/durability create` rejected sound IDs containing `:` or `.`
- Mod icon was missing from the mod list
- Menu errors were sent to chat behind the screen instead of shown on it
- Removed leftover template mixins
- LICENSE file contradicted the declared license