Refine reader documentation and output contracts

Unify documentation names across the release

Show four MP4 demos and expand section-level documentation links

Add inline animated demo previews

Refresh reader-first model card and repair demo audio duration

Finalize evaluation versions and six-metric results

Use explicit SAID model identifiers in public commands

Unify demo outputs and document AudioMAE demo

Document class-agnostic release and checkpoint defaults

Release Audio2Sph and Panoramic Decoder checkpoint

Document project-local checkpoint directory

Document automatic checkpoint download

Add SAID documentation and media