fix(core): fit the shadow map to the visible frustum at high pitch (3/5) - #10893

…/5) (#10893)

* fix(core): release shadow resources when LightingEffect turns shadows off

EffectManager reuses the existing LightingEffect and calls setProps when
a new one is passed. Turning the last `_shadow` light off kept the
shadow module registered as a default module, but getShaderModuleProps
stopped passing the dummy shadow map, so shadow_uShadowMap0/1 were
unbound and every layer skipped drawing. Call cleanup() from setProps
when no light casts shadows, so layers are rebuilt without the module.

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

* fix(core): draw the shadow map without per-layer polygon offset

Layer._drawLayer applies `getPolygonOffset` (default [0, -layerIndex * 100])
in every pass. The shadow map stores gl_FragCoord.z, which includes the
offset, so the k-th layer drawn in the shadow pass stored a depth
k * 100 * 2^-16 closer to the light. From the third layer on, layers fell
partly or fully into their own shadow. ShadowPass now sets depthBias: 0
so the shadow map is drawn without the offset.

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

* fix(core): fit the shadow map to the visible frustum at high pitch

getViewProjectionMatrices fitted the light frustum to the points where the
viewport corner rays hit the ground. With the default fov, the top corners
reach the horizon at pitch ~71.6. Just below it the hits are far beyond the
camera's far plane (light frustum 20 x 28 km at pitch 72, 63 m texels).
Above it they are behind the camera, so the shadow map no longer covers the
visible scene. Shadows disappear, and fragments past the light frustum's far
plane are always shadowed (black areas).

Fit the light frustum to the view frustum clipped to z >= 0 instead: the
frustum corners above the ground plus the points where frustum edges cross
the ground. When every corner ray hits the ground before the far plane, this
gives the same points as before.

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

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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit d610287)