Fix spot light degenerate outer angle

[Saratii]

Objective

• Fixes spotlight produces garbage artifacts when outer angle and inner angle are set to zero and shadowmaps enabled #25360
• A SpotLight with outer_angle of 0.0 renders garbage when shadow_maps_enabled is set, and a SpotLight with outer_angle at or near PI / 2.0 disappears entirely, even though it logs that it is being clamped.

Solution

tan(outer_angle) is the scale of the cone's perspective projection, and both ends of the old range broke it:

• 0.0 → scale 0, so the shadow map projection and the shader's shadow lookup divide by zero.
• Old clamp PI / 2.0 - 1e-4 → scale ~10000, collapsing the cone into a few texels at the shadow map centre, so the nearest occluder shadows everything.
• Exactly PI / 2.0 → f32(PI / 2.0) rounds above true π/2, so tan is -2.3e7 and the projection inverts.

Adds SpotLight::MIN_OUTER_ANGLE (1e-3), MAX_OUTER_ANGLE (1.5 rad, ~85.9°, still ~1 shadow texel per degree at 2048), and clamped_angles(), which clamps both angles, keeps inner <= outer, and maps NaN to the minimum. Cluster assignment and the shadow map frustum used the raw angle before, so they disagreed with what the shadow map was rendered with.

Drops the warn_once! in extract_lights: it fired once per process and named a clamp target that didn't work. Clamping is silent; clamped_angles() reports what's rendered. The warning was also logically inconsistent if the spotlight goes from invalid to valid to invalid again.

Testing

• Unit test: clamped angles stay in range and keep the projection finite for 0.0, -1.0, NaN, PI / 2.0, 100.0.
• Behaves correctly in minimal reproduction at both pi/2 and 0.

Recording.2026-08-11.153411.mp4