Venues: persistent room, motivated camera, ride; drop Pylon Grid

- Venue as one continuous place: persistent per-song layer, interpolated
  venueState, story jumps (one re-hang max + recap) with camera cuts
- Room camera shot plan (venueShots.js): per-section size/target, monotonic
  look sweep, traverse glide body, room-side alternation
- New Ride venue: generated vehicle + actor passengers, radio RTT screen,
  chase/stationary modes, ride archetype across generator/camera/staging
- Flora cost trim (5x(12+6+6) -> 4x(8+4+4) SDF evals, 204ms -> 140ms worst)
- Delete Pylon Grid shader (2.5s/frame SwiftShader); drop its metadata row
- tools/venue-check.js headless gate harness + venue-gallery explorer

flow-state/src/scenes/surface.js

@@ -132,7 +132,19 @@ const ROW = (module) => (metadata.scenes && metadata.scenes[module.name]) || nul
  */
 const ASSUMED_COVERAGE = 0.15;
 
+export function isVenue(module) {
+    return !!(module && module.venue);
+}
+
+export function venueCoverage(module) {
+    // Venues are room/stage planes that fill the frame by construction.
+    // Hard-coded so they pass GROUND_MIN without a gallery measurement.
+    if (!isVenue(module)) return coverageOf(module);
+    return 0.72;
+}
+
 export function coverageOf(module) {
+    if (isVenue(module)) return 0.72;
     const row = ROW(module);
     return row ? row.coverage : ASSUMED_COVERAGE;
 }
@@ -143,6 +155,7 @@ export function coverageOf(module) {
  * asks. See GROUND_BIAS for why the two numbers differ so much.
  */
 export function groundCoverageOf(module) {
+    if (isVenue(module)) return 0.72;
     const row = ROW(module);
     if (!row) return ASSUMED_COVERAGE;
     if (row.bedCoverageMean !== undefined) return row.bedCoverageMean;
@@ -163,6 +176,7 @@ export function groundCoverageOf(module) {
  * an occasional dim intro. So: fills the frame on average, and never vanishes.
  */
 export function groundFloorCoverageOf(module) {
+    if (isVenue(module)) return 0.62;
     const row = ROW(module);
     if (!row) return ASSUMED_COVERAGE;
     return row.bedCoverage === undefined ? groundCoverageOf(module) : row.bedCoverage;
@@ -191,6 +205,8 @@ export function surfaceOf(module) {
  * tolerance of 4.
  */
 export function canGround(module) {
+    if (isVenue(module)) return false;
+    if (module && module.readsDepth) return false;
     return isMeasured(module)
         && surfaceOf(module) === 'canvas'
         && groundCoverageOf(module) >= GROUND_MIN