[BUG FIX] Derive BatchRenderer texture descriptor capacity from scene textures

[NoahLinckeScout]

Description

Replace the fixed 128-texture descriptor capacity with a per-scene capacity
derived from GSModel.numTextures before RenderContext creates pipelines or
descriptor sets.

The change:

• adds maxTextures to RenderManager::Config and initializes it from the
  loaded scene, with a minimum capacity of one;
• applies that capacity to the regular draw path, BatchRenderer draw path,
  viewer voxel path, descriptor pool, and descriptor-set layout;
• validates the requested capacity against Vulkan sampled-image limits before
  pipeline construction; and
• makes loadObjects fail with an actionable error if a later load exceeds the
  configured capacity.

There is no Python API change. Existing scenes retain the same behavior; scenes
with more than 128 textures now use valid descriptor layouts when supported by
the device.

Related Issue

Resolves #55

Motivation and Context

loadObjects previously wrote one sampled-image descriptor for every source
texture into a binding created with capacity 128. Vulkan requires that the
descriptor write fit the binding. Exceeding that limit produced missing textured
geometry and native allocator aborts.

How Has This Been / Can This Be Tested?

The issue's linked repro.py is self-contained: it generates a 256-texture
GLB and runs in a clean uv environment using the released public packages.

uv run repro.py

Before this change, the script reports 152/256 visible textured quads and the
child renderer aborts. With this change, the same script reports 256/256 and
the renderer exits zero.

The patch was also checked against the current main revision
754c5aa7b4214e70152db56ef012305d5fb27f2e.

Screenshots (if appropriate)

The issue repro generates synthetic unpatched and patched images containing
only colored-quad fixture geometry.

Checklist:

• I read the CONTRIBUTING document.
• I followed the Submitting Code Changes section of CONTRIBUTING.
• I tagged the title correctly (including BUG FIX/FEATURE/MISC/BREAKING).
• I updated the documentation accordingly or no change is needed.
• I tested my changes and added instructions on how to test them for reviewers.
• I have added tests to cover my changes.
• All new and existing tests passed.