Dungeon style chicken coops and dormitory beds

[Rokk001]

Problem

The chicken coops have a bright red roof and the dormitory beds (imp and spider beds in particular) look like spiky lumps, which does not fit the dark dungeon look of the rest of the game.

Change

• Chicken coop: dark slate roof and greyed rough wood instead of the bright red roof (ChickenCoop.png recoloured by tools/room-objects/restyle_chicken_coop.py).
• Standard bed (used by 15 creatures): darker oak, coarse blanket, new linen material, no gloss stripe (Bed.material).
• Imp and spider beds: new low-poly meshes (iron frame with horn posts, straw and rust blanket / bone frame, pad and silk cocoon) replacing the lumps, same 1x1 footprint, single-pass materials (generated by tools/room-objects/generate_beds.py). The now unused normal maps and SpiderBedWeb.material are removed.
• Other bed meshes are unchanged. New assets are listed in CREDITS.

Visual change only; no gameplay, network or save effect.

Dependencies

None. One commit on top of shaders-improvement, no file overlap with the open bed or dormitory PRs (#178, #179, #180, #195). The new imp and spider bed orientation (#178 touches bed alignment) has not been checked in game together with #178.

Verification

Offline renders before and after, and Mario's in-game screenshots of a chicken farm and a dormitory (below). The Release build succeeds.

Chicken coops, before and after:

Beds, before and after:

In game, chicken farm and dormitory:

[Rokk001]

Replaced by #338, which contains the same changes.