Door sprite — swap castle gate for 1-tile FG_Village cabin door

The previous 32×32 FG_Fortress arched gate at (4,19) was rejected as 'a
door for a entrance to a castle' — too imposing for a cabin's front door.

Pivot: FG_Village atlas (3, 24) — a single 16×16 olive-wood plank door
with a white U-handle, extracted from the red-roofed cottage template.
Sprite occupies one tile (no overhang, no rising lintel), bottom-anchored
the same as Wall so Y-sort layers pawns correctly.

Verified in MCP play_scene: the door slots cleanly into the demo cabin's
south-wall gap at (47, 28), matching the surrounding stone-brick wall
height. Ghost-alpha pipeline (0.4 in-build → 1.0 on _complete) intact.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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