player: add equipment slots and inventory overlay

- Weapon/armor equip slots persist until replaced
- Numbered inventory overlay with I key
- E to equip from inventory, U to use potions"

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I474acd676da3b768c1aac24f75f303e86a6a6964

src/render.h

@@ -18,6 +18,9 @@ void render_items(const Item *items, int count);
 // Render UI overlay
 void render_ui(const Player *p);
 
+// Render inventory selection overlay
+void render_inventory_overlay(const Player *p, int selected);
+
 // Render game over screen
 void render_game_over(void);