Restore configurable texture filtering

[themuffinator]

Fixes #121.

What changed

• restores the archived image_filter renderer CVar with all six Quake 4 filter names and console completion
• applies the selected TF_DEFAULT sampling mode in both OpenGL and Vulkan
• refreshes loaded default samplers immediately when image_filter or image_anisotropy changes
• keeps explicitly authored sampler states intact and disables anisotropy for nearest-texel modes
• documents the pixelated-texture command and adds a validation contract

Validation

• python tools/tests/renderer_texture_filter.py
• full Windows x64 Meson compile, including client, dedicated server, SP/MP modules, renderer-gl, and renderer-vk
• windowed SP game/airdefense1 gameplay through renderer_gameplay_benchmark.py, with image_filter=GL_NEAREST_MIPMAP_NEAREST: 1/1 pass, live sampler refresh logged, engine-render-target screenshot captured
• git diff --check

The broader settings_menu_coverage.py check is currently blocked in this workspace by the companion openQ4-game main checkout lacking its expected MP net_menulanserver declaration; that pre-existing repository-alignment failure is unrelated to these renderer changes.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reclaim stale Vulkan samplers when settings change

When Vulkan users repeatedly switch image_filter or adjust image_anisotropy, each mode/anisotropy/repeat/mip combination is retained until device shutdown because the new mode is part of the cache key. Refreshing all loaded default-filter images can therefore consume the fixed 64-entry cache during a normal session; subsequent misses return vkSamplers[0], applying an unrelated filter or address mode to textures. Evict stale default samplers or otherwise bound/reuse these setting-dependent entries.

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