docs: Add extended format hardening spec and clean up stale submodules

- Add docs/HARDENING_EXTRAS.md with comprehensive hardening specification for additional formats (AVIF, JXL, TIFF, OpenEXR, MPEG-TS) and hidden-path components (ICC, metadata, fonts)
- Define CPU-tuned hardening flags for Intel Core Ultra 7 165H (Meteor Lake)
- Remove stale libjpeg-turbo and libpng submodule entries
- Re-initialize all active submodules (ffmpeg, flac, ogg, opus, vorbis)

Author: claude