Feature(GPU): Texture dumper and replacer

[Graine25]

This feature adds a texture dump and replacement system that identifies guest textures by a stable content hash, dumps them to textures/dump, and loads user-authored replacements from textures/replace. When enabled through CVars, matching replacements are decoded to RGBA8 and injected into the D3D12 texture cache in place of the original guest texture.

• build(thirdparty): expose stb_image target - Adds stb_image as an available third-party target and updates install handling so the replacement pipeline can decode image files, especially PNG replacements, without embedding a separate image dependency path.

• a8517da feat(gpu): add texture replacement pipeline - Introduces the core replacement/dumper module under graphics/pipeline/texture. This adds hashing, replacement directory scanning, PNG/DDS loading, DDS dumping, guest texture untiling/endian conversion for dumps, and the filesystem layout: textures/dump for generated assets and textures/replace for user-provided replacements.

• 7a90eaa feat(gpu): inject replacement textures - Wires the replacement pipeline into the texture cache and D3D12 upload path. It hashes guest texture contents, looks up matching replacement files, adjusts the texture key for RGBA8 replacement uploads, preserves the original guest layout for memory watches, and keeps temporary upload buffers alive until the GPU has finished using them.

• feat(gpu): add texture replacement cvars - This commit adds the user-facing controls for the texture edit feature: texture_dump_enabled, texture_replace_enabled, and texture_folder. Dumping and replacement are now gated by CVars, and texture_folder lets users choose a custom root directory for dump/ and replace/ instead of always using <executable folder>/textures.

More effort can be made to implement this into Vulkan as well as adjusting for more DDS formats or even PNG's, but this has mostly been optmized for D3D12. Almost all work is @SolarCookies. Addresses issue #294