chore(meta): add event background scene-class overlays to asset-gen

Add 5 scene-class overlays for event backgrounds: Noble interior
(bright marble, colored fabrics, candlelight), Institutional interior
(cold stone, iron fixtures), Noble arena (Colosseum-style fighting
pit with house banners), Skaa/underclass (ash-stained, cramped),
and Exterior (overcast Scadrial landscape). Scene-class mapping
table routes each event scene to its overlay. Noble interiors use
bright marble instead of dark mahogany to contrast wealth against
the ash-choked exterior world.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/asset-gen/references/category-templates.md

@@ -73,12 +73,74 @@ with mist, ash particles, and volumetric light. Characters at mid-distance. Dark
 ```
 
 ### Event scene backgrounds (1592x848, 16:9)
+
+Base template (shared by all event backgrounds):
 ```
 CK3 event background: a wide atmospheric environment with no characters in the scene — this
-is a backdrop only. Rich environmental detail, strong mood lighting. Ash, mist, or
-candlelight depending on setting. A place where dramatic events unfold.
+is a backdrop only. Rich environmental detail, strong mood lighting. 16:9 cinematic
+composition with depth — foreground detail, mid-ground subject, atmospheric background
+fading into haze. Dark vignetting at edges. A place where dramatic events unfold.
+Absolutely no people, no characters, no figures.
 ```
 
+Combine the base template with ONE of the following scene-class overlays:
+
+#### Noble interior (court, ball, private_chamber)
+```
+Opulent noble interior. Polished pale marble floors and columns, white-veined stone walls
+kept immaculately clean — brightness itself is a display of wealth in this ash-choked world.
+Rich colored fabrics in deep crimsons, golds, and blues — rare color in a grey world. Brass
+and steel fixtures gleaming with polish, ornate metalwork filigree. Warm golden candlelight
+from chandeliers, multiple light sources creating a bright, warm interior. Tall arched
+windows showing ash and darkness outside — the contrast between interior luxury and exterior
+bleakness is the point. Metal ornamentation everywhere — in this world, metal IS wealth.
+Clean, bright, and warm inside; grey, ashy, and cold outside.
+```
+
+#### Institutional interior (temple, dungeon, ruins)
+```
+Austere institutional interior. Cold stone walls, iron fixtures, functional architecture.
+Sparse and imposing — authority expressed through scale and bareness, not decoration.
+Torchlight or brazier glow. Smoke and incense haze replacing outdoor mist. Steel Ministry
+or secretive order aesthetic — order, control, rigid geometry.
+```
+
+#### Skaa / underclass (streets, plantation, fighting_pit, underground, market)
+```
+Impoverished and oppressed setting. Crumbling ash-stained walls, rough timber, packed dirt
+floors. Dim torchlight or grey overcast daylight filtering through soot-caked openings.
+Everything coated in a fine layer of volcanic ash. Threadbare, makeshift, salvaged materials.
+Sharp contrast to noble opulence — no metal ornamentation here, metal is too precious.
+Cramped, crowded, desperate. The weight of the Final Empire visible in every surface.
+```
+
+#### Exterior (wilderness, battlefield, mists, ashmount_close, clear_night)
+```
+Exterior Scadrial landscape. Perpetually overcast sky with red-brown clouds. Volcanic ash
+falling like grey snow. Thick mist clinging to the ground. Barren vegetation — brown scrub,
+no green. Distant ashmounts on the horizon trailing smoke. Oppressive atmosphere but with a
+stark, bleak beauty.
+```
+
+#### Noble arena (fighting_pit)
+```
+Grand stone arena built for noble entertainment. Tiered stone seating rising
+high, with ornate private viewing boxes draped in colored fabrics for the Great
+Houses. Iron cage or pit floor below — bloodstained sand and scattered weapons.
+Brazier light and torchlight from iron sconces. The architecture is imposing and
+wealthy but the purpose is brutal — Roman Colosseum meets dark fantasy. Metal
+railings, house banners, the contrast of noble opulence watching savage violence.
+```
+
+Scene-class mapping:
+| Scene | Class |
+|-------|-------|
+| court, ball, private_chamber | Noble interior |
+| temple, dungeon, ruins | Institutional interior |
+| fighting_pit | Noble arena |
+| streets, plantation, underground, market | Skaa / underclass |
+| wilderness, battlefield, mists, ashmount_close, clear_night | Exterior |
+
 ### Activity header backgrounds (1100x440, 5:2)
 ```
 CK3 activity header: wide panoramic scene of the activity in progress. Painterly, dramatic