✨ add Buildings wiki page

Buildings.md

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+# Buildings
+
+> **Legend**
+> - ✅ Implemented — exists in the current codebase
+> - 🗺️ Planned — design exists but not yet implemented
+
+---
+
+All buildings are placed by the player (press **B** to open build menu). Costs are deducted from the stockpile.
+
+| Building | Cost | Tile effect | Function |
+|----------|------|-------------|----------|
+| `floor` ✅ | 2 wood | GRASS → FLOOR | Walkable platform |
+| `wall` ✅ | 3 wood + 1 stone | GRASS → WALL | Impassable barrier |
+| `chest` ✅ | 5 wood + 2 stone | GRASS → FLOOR | Visual only (no gameplay function yet) |
+| `bed` ✅ | 6 wood | — | Villager spawn point + sleep location |
+| `stockpile_zone` ✅ | free | — | Villagers deposit items here |
+
+## Placement Rules ✅
+
+Cannot build on:
+- Impassable tiles (water, FOREST, ROCK, WALL)
+- Existing buildings
+- Resource nodes
+- If stockpile has insufficient resources
+
+## Notes
+
+- **Beds** are the population cap — one villager per bed. Without a free bed, no new villagers spawn.
+- **Stockpile zones** have no cost and no tile effect; they are invisible markers that villagers pathfind to when depositing items.
+- **Chests** are currently visual only — item storage is global (the stockpile), not per-chest.
+
+---
+
+← [[Game Systems Reference]]