Add two-stage charged-crystal demo and original art set.

assets/generated/STYLE.md

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+# Mana Foundry original art contract
+
+All generated icons, renders, and materials replace Kenney Factory Kit in the playable demo. The recipe book remains the ID authority; this folder is the art authority.
+
+## Shared look
+
+- Dark stone, aged brass, cyan ley-line light, violet high-tier charge.
+- Each biome only tints the accent, never the treatment: old kingdom cyan, forest sap-green, death soul-violet, ember slag-orange, mirror star-silver, rift gold, post-rift magenta.
+- No letters, numbers, UI chrome, watermark, or photographic people.
+- Isolated subject, generous margin, no ground plane, no baked contact shadow.
+
+## Icons (`icons/items`)
+
+- Hand-painted fantasy factory inventory icon.
+- Three-quarter object view, solid fill with a thin dark-stone rim, same visual weight.
+- Flat charcoal field `#1A1612`.
+- Must read at 32px: one silhouette, one accent glow.
+
+## Renders (`renders`)
+
+- Same orthographic south-east factory camera as the Godot scene (elevated, no perspective).
+- Machines sit on a hidden grid cell; the building is the only subject.
+- Logistics pieces match machine scale so a belt cell and a hopper share the same footprint language.
+
+## Materials (`materials`)
+
+- Seamless painted tiles, non-directional lighting, no landmark motifs.
+- Used as albedo/emission sources, not as Kenney colormap swaps.
+
+## Known defects
+
+- Several materials inherit the factory-stone crack layout, so a 2×2 tile of `aged_brass` still shows a seam.
+- A few late-game icons (`clay_construct`, `walker_construct`) read more sculpted than the painted crystal set, though they keep the charcoal field and padding.
+- Demo belt items map `raw_crystal` → `raw_mana_crystal`, `refined_crystal` → `awakened_crystal`, `charged_crystal` → `charged_phase_medium`, because the recipe book has no separate charged-crystal row.