Dungeon themes: per-song visual identity (crypt/overgrown/ember/flooded/windswept)

One album must not render the same dungeon twice. dungeonTheme() scores
the measured summary per theme — pace terms gate on tempoConfidence so
doubled detectors never read fast, crypt is penalised for blazing
masters — plus small seeded jitter so ambiguous songs vary across seeds
while decided races stay decided. The plan carries the theme name;
dressing mix, planting/timber/puddle densities follow it, and the facade
builds all materials (stone/floor multipliers, torch + light color, wood,
fog tint) from the same record.

Calibrated bank spread is 4/4/4/4/1 (windswept holds runner); corners
stable across seeds; plan reshaping, facade wiring, and murk-vs-clear
gates covered by tests.

flow-state/DESIGN.md

@@ -124,6 +124,17 @@ Actors and objects change only at camera cuts:
 - Absolute animation speed follows the song: motion bias is
   tempo-dominated and every `rate: true` param scales by per-track
   `rateScale` — slow songs got fast scenes before this.
+- Venues have a per-track **character** the same way: the dungeon derives
+  sealed/murky/big (`dungeonCharacter`: tonal darkness, doubling-compensated
+  tempo, stillness, weight) from the measured summary, calibrated against
+  the bank because arrangement intent doesn't survive measurement (ambient
+  doubles tempo, hiss reads bright). Dark slow songs seal fully indoor;
+  blazing masters always crack open.
+- The dungeon also gets a per-track visual **theme** (`dungeonTheme`:
+  crypt/overgrown/ember/flooded/windswept), scored off the same summary
+  traits — one album must not render the same dungeon twice. Pace terms
+  gate on tempoConfidence (doubled detectors must not read fast), jitter
+  is small enough that decided races stay decided across seeds.
 
 ## 7. Grounds and composition