[nai62]

• Add AVIF loading, file-picker and Explorer associations, and single-DLL Windows packaging with CI coverage on Windows and Linux.
• Display animated AVIF as a decoded first frame only. Require an available AVIF plug-in for file listings, with regression tests for animation, corrupt payloads, auto-detection, and missing plug-ins.
• Document the existing HDR/wide-gamut color limitations and plug-in setup.
• Checked Windows Debug/Release builds and 375 cases across fileloader, viewernavigation, and windowstartup (no failures or skips). Existing PCH warnings remain. NSIS installer generation and interactive GUI checks are still unverified.