Release Candidate 2 for Beta 2

Second release candidate for Beta 2, built from main at 5d7a26aa599cb6dab3d387ccef77e49846cb4d55.

Fixes

• Correct Linux embedded Vulkan viewport creation, Qt/SDL video-driver selection, Wayland resizing, and packed shader/camera orientation.
• Preserve Qt-owned X11 viewport geometry so the renderer does not overlap the toolbar or leave an uncovered strip.
• Rebuild invalid cached shaders and pipelines after viewport runtime reload, and recreate fullscreen buffers and fallback textures with their window (#260, #261).
• Protect GPU resources during frame reuse, resizing, and editor scene reload.
• Correct Vulkan SSR, SSAO, and motion-vector coordinates and avoid unsupported depth-mipmap generation.
• Bundle Windows runtime dependencies and launch the editor as a GUI application.
• Repair Photon transmission, dielectric shading normals, spectral reflectance, and material-preview resource handling.
• Improve model and texture caching, tetrahedralization caching, collider validation, deferred target allocation, and shadow sampling.
• Consolidate the release fixes and canonical Opal dependency on main.

Validation

All four assets and the native, CLI, and formatting checks passed for this exact main commit in the official packaging workflow. The unmodified Linux ARM package was tested on Ubuntu 25.10 with X11/Openbox and Wayland/Weston: PBR startup, viewport dock resizing, and runtime reload passed with the validation layer enabled, without the prior linked-shader failure or GPU resource-in-use errors. Native Windows PBR-project verification remains pending in #239; the reporter cannot test Windows currently. Dense grid overlay artifacts were observed with the Linux software Vulkan renderer (Mesa llvmpipe); hardware GPU behavior was not verified in that environment.

Full changelog: beta2rc1...beta2rc2