Eclipse Expansion

## v0.4 - The Umbral Update

### Blocks
- Added Threshold Stone (crafted with Deepslate + Eclipse Essence)
- Added Threshold Cobblestone
- Added Threshold Bricks (stairs, slab, wall)
- Added Cracked Threshold Bricks (stairs, slab, wall) — obtained by smelting Threshold Bricks
- Added Threshold Torch
- Added Eclipse Altar — special block used to invoke the eclipse through a ritual
- Added Eclipse Pedestal — required for the altar ritual

### Items
- Added Corrupted Solar Fragment — required to activate the eclipse ritual
- Added Eclipse Essence — base material for crafting Threshold blocks

### Eclipse Ritual
- Place 4 Eclipse Pedestals around the Eclipse Altar and load them with Eclipse Essence
- Use a Corrupted Solar Fragment on the Altar to manually invoke the eclipse

### World Generation
- Added 4 structures that generate in the Valle del Eclipse biome:
  - Altar — ritual site
  - Ruins — ancient ruins
  - Explorer Camp — explorer camp
  - Eclipse Cult — underground cult structure

### Art
- Added 6 custom paintings:
  - El Ritual
  - El Culto
  - La Adoración
  - El Errante
  - La Entidad
  - El Valle

### Recipes
- Added crafting recipes for all Threshold stone blocks, stairs, slabs and walls