Fix default post-processing brightness (0 → 1)

[Copilot]

grading.brightness defaulted to 0 (black), making post-processing produce a completely black scene when enabled. The neutral/identity default should be 1, consistent with contrast and saturation which already default to 1.

// src/splat-serialize.ts
grading: { enabled: false, brightness: 1, contrast: 1, saturation: 1, tint: [1, 1, 1] },

Original prompt

Repository: playcanvas/supersplat

Goal: Create a pull request that changes the default post-processing brightness from 0 to 1.

Details:

• Update defaultPostEffectSettings in src/splat-serialize.ts so that grading.brightness defaults to 1 instead of 0.
• Keep all other default settings unchanged.
• Ensure TypeScript formatting/linting remains consistent with the existing file.
• Add a concise PR title and description explaining the change and why.

Reference file and commit:

• File: src/splat-serialize.ts
• URL: https://github.com/playcanvas/supersplat/blob/8189616eee2fa40260a227a782552619e9f7ae99/src/splat-serialize.ts

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: Can you change the default brightness to 1 and create a pullr equest

Assistant: I’m waiting for your confirmation in the GitHub dialog to proceed with creating the pull request that changes defaultPostEffectSettings.grading.brightness from 0 to 1.

This pull request was created from Copilot chat.

[abstrakt8]

In Studio, the brightness would always be default to 0, which would make the screen dark