docs(design): RimWorld world-map fluency reference — screenshot + extracted-techniques note (T-1175)

Jeroen's benchmark capture for the Atlas polish pass, saved in-repo
with the technique extraction (rivers-as-networks/taper, road-vs-river
color+straightness disambiguation, coast gradient, data-driven stipple,
labels) so the future Araminta-led pass has the source material.

Tickets: T-1175

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/design/references/README.md

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+# Design references
+
+External visual references collected for design/polish passes. Each image
+gets a one-paragraph note here: what it is, why it was captured, and which
+ticket/pass consumes it.
+
+## rimworld-world-map-fluency.jpg
+
+RimWorld world map (starting-site selection screen), captured by Jeroen
+2026-07-23 during the T-1170 river-course batch as the **map-fluency
+benchmark** for the Atlas polish pass (**T-1175**): *"the rimworld maps do
+roads, rivers, coasts and biomes quite well"* — with the explicit caveat that
+its hex substrate and globe projection are **not** us; the techniques
+transfer, the tiling doesn't. Extracted techniques (full list on T-1175):
+rivers as converging networks with subtle width variation and taper-to-source;
+roads vs rivers disambiguated by color + straightness rather than width;
+coasts as a shoreline gradient (beach band + near-shore water shading);
+biome/relief **texture** — stipple density carrying hills/mountains/forest on
+top of hue (maps onto T-1162's derived patchiness/relief fields: texture as
+data, not decoration); and geographic labels (our T-1169) doing heavy
+fluency lifting.