Iso 2.0 [1/12]: Base Biome Tile Rendering (128px → 256×128 diamond)

[putersdcat]

Spec reference

IsoRenderingPlanV2.1.md §Phase 2 — Tile rendering; §3.1 Base Tile

Goal

All 6 base biome tile types render as proper 256×128 iso diamonds with correct
colors and no stretch artifacts:

• grass, dirt, rock, water, sand, dry-grass

Technical requirements

• MicroTile SVG is 128×128.
• Rendered via flat iso projection: ctx.transform(1, 0.5, -1, 0.5, cx, topY)
• Result diamond: 256px wide, 128px tall, clipped to diamond shape.
• Tile color palette must pass visual inspection vs spec §3.1 table.

Acceptance criteria (ALL required to close)

• render_nano_scene with a 5×5 grid of each biome type produces a clean single-biome canvas (6 PNGs).
• Diamond edges are sharp (no sub-pixel bleed).
• Each PNG saved to ProgressEvaluations/biome-{name}-5x5.png and committed.
• Commit SHA referenced in issue comment.

Verification command

render_nano_scene entries=[{kind:"grass",col:0,row:0},...] width=512 height=400 outputPath=ProgressEvaluations/biome-grass-5x5.png
Repeat for all 6 biomes.