fix(legacy): sphere light has not lighting at LDR mode

[troublemaker52025]

Re: #

Changelog

• sphere-light.ts 中，luminanceLDR 只有 setter 没有 getter；而 updateUbo 却调用了未定义的 getLuminanceLDR，在 ts 中，未定义的 get 返回 undefine 传入到 GPU 就是NaN, 光照完全失效
• https://forum.cocos.org/t/topic/161540
• skybox LDR cocos-engine#17631

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Continuous Integration

This pull request:

• needs automatic test cases check.

  Manual trigger with @cocos-robot run test cases afterward.

• does not change any runtime related code or build configuration

  If any reviewer thinks the CI checks are needed, please uncheck this option, then close and reopen the issue.

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Compatibility Check

This pull request:

• changes public API, and have ensured backward compatibility with deprecated features.
• affects platform compatibility, e.g. system version, browser version, platform sdk version, platform toolchain, language version, hardware compatibility etc.
• affects file structure of the build package or build configuration which requires user project upgrade.
• introduces breaking changes, please list all changes, affected features and the scope of violation.

[troublemaker52025]

@cocos-robot run test cases

[Copilot]

Pull request overview

This PR fixes a rendering bug in LDR mode for legacy light types by adding missing luminanceLDR getters so that code reading the property (e.g., UBO packing) no longer receives undefined (which can propagate as NaN).

Changes:

• Add get luminanceLDR() to SphereLight so LDR luminance reads correctly.
• Add get luminanceLDR() to PointLight for the same reason and consistency with other light implementations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cocos/render-scene/scene/sphere-light.ts	Adds the missing luminanceLDR getter so LDR luminance reads don’t return undefined.
cocos/render-scene/scene/point-light.ts	Adds the missing luminanceLDR getter to prevent undefined reads and align with other light classes.

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[github-actions]

Code Size Check Report

Wechat (WASM)	Before	After	Diff
2D Empty (legacy pipeline)	1014561 bytes	1014634 bytes	⚠️ +73 bytes
2D All (legacy pipeline)	2682237 bytes	2682310 bytes	⚠️ +73 bytes
2D All (new pipeline)	2774076 bytes	2774149 bytes	⚠️ +73 bytes
(2D + 3D) All	10031391 bytes	10031464 bytes	⚠️ +73 bytes

Web (WASM + ASMJS)	Before	After	Diff
(2D + 3D) All	16867805 bytes	16867878 bytes	⚠️ +73 bytes

Interface Check Report

! WARNING this pull request has changed these public interfaces:

@@ -13006,8 +13006,9 @@
                 /**
                  * @en The luminance of the light source in LDR mode
                  * @zh LDR 模式下光源的亮度
                  */
+                get luminanceLDR(): number;
                 set luminanceLDR(value: number);
                 /**
                  * @en The AABB bounding box of the lighting area
                  * @zh 受光源影响范围的 AABB 包围盒
@@ -13181,8 +13182,9 @@
                 /**
                  * @en The luminance of the light source in LDR mode.
                  * @zh LDR 模式下光源的亮度。
                  */
+                get luminanceLDR(): number;
                 set luminanceLDR(value: number);
                 /**
                  * @en The AABB bounding box of the lighting area.
                  * @zh 受光源影响范围的 AABB 包围盒。

[troublemaker52025]

测试方法：

• 打开cocos-test-projects/lighting/lighting-ldr 场景，旧版本没有球面光光照效果

*测试场景需要合并
cocos/cocos-test-projects#944

[troublemaker52025]