fix(assets): mountain rock could never fire — kelvin compared to 0.35 (T-1295)

compute_biome receives absolute kelvin (the Whittaker table is kelvin; the
0-1 normalisation happens afterwards in simulate(), for the renderer only),
but two terrain rules compared it to 0.35. That was the case from the
generator's first commit (f84275edf):

- mountain rock, `temperature < 0.35`: never true, so the class never
  appeared through this rule on any body;
- sulfuric scrub, `temperature > 0.35`: always true.

0.35 can only mean a fraction of the world's own range, the normalisation
compute_moisture already uses, so both rules now compare against that. A
world with no temperature range reads 0 (the cold end).

tooling/test_planet_biome_rules.py pins the rule both ways on a synthetic
body: cold high ground turns to rock (>90%, since anomaly scatter repaints
~3%), and warm high ground and low ground do not. Mutation-proven: restoring
the kelvin comparison fails it at a rock share of exactly 0.000. Wired into
make test-tooling.

Sulfuric scrub remains unreachable for a different reason: it converts rock
only at elev_norm 0.25-0.65, and rock exists only above 0.65. It is left as
found, since making it reachable is a design call and belongs to the balancing
pass, so it is not pinned.

Found while shaping the D-258 biome bake. The committed reliefmaps and globes
were rendered with the bug, and the coming bake reflects the fix.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Makefile

@@ -293,6 +293,9 @@ test-tooling:
 	@echo "  [test-tooling] oasis ring-scaling pin (T-964, PR #210 review)..."
 	@$(VENV_PY) tooling/test_planet_oasis_rings.py 2> .cache/test-tooling-oasis-ring.log || \
 		{ echo "  FAIL: oasis ring scaling — log follows:"; cat .cache/test-tooling-oasis-ring.log; exit 1; }
+	@echo "  [test-tooling] mountain-rock rule compares on the world's own scale (T-1295)..."
+	@$(VENV_PY) tooling/test_planet_biome_rules.py 2> .cache/test-tooling-biome-rules.log || \
+		{ echo "  FAIL: biome rules — log follows:"; cat .cache/test-tooling-biome-rules.log; exit 1; }
 	@echo "  [test-tooling] reach atlas planet options vs module parsers (T-1288)..."
 	@$(VENV_PY) tooling/test_planet_router.py 2> .cache/test-tooling-planet-router.log || \
 		{ echo "  FAIL: planet router drift — log follows:"; cat .cache/test-tooling-planet-router.log; exit 1; }