Update README: q6q8 replaces broken q4q6, add WER validation table

Remove em dash

Simplify README for end users -- drop internal PSNR/CLI-flag build details

Rewrite README: drop Argmax mirroring language, list our own turbo fp16 + quantized q4q6 builds

docs: rewrite as Diction-owned build, drop mirror/1:1 framing

Card: per-variant provenance; turbo is redistributed from Argmax, not ours

Add model card: usage, variants, provenance