Fix shader: remove leftover window.__flightDir references

Old shader code with fdx/fdz still referenced window.__flightDir,
which GLSL can't parse. Removed those lines. Now shader uses only
uFlightDir uniform passed from JS.

vendor/clouds3d.js

@@ -140,10 +140,7 @@ var FRAG_SRC = [
         'float drift = uTime * uSpeed * 0.12;',
         // Fixed altitude well above the cloud ceiling (y=1.5).
         'float camY = 2.2;',
-        // Camera position follows window.__flightDir (set from URL #flight=...).
-        // Default: drift along +Z (north). For east: drift along +X. For south: -Z, etc.
-        'float fdx = (window.__flightDir ? window.__flightDir.dx : 0.0);',
-        'float fdz = (window.__flightDir ? window.__flightDir.dz : 1.0);',
+        // Camera position uses uFlightDir uniform (set from JS each frame).
         'vec3 ro = vec3(drift * uFlightDir.x, camY, drift * uFlightDir.y);',
         // Ray direction: tilt more downward so the visible ground fits
         // within the mosaic. At uv.y = 0 the ray goes ~26° below