docs: open primary AT validation campaign

[mattheliu]

Outcome

Opens the exact DSH 0.1.2-alpha.2 primary human-validation campaign after every public-availability gate passed anonymously.

Verified before opening

• exact core and lab revisions are publicly readable
• default-branch manifest, bilingual guides, automated report, and four intake forms are public
• Discussion 16 and Issues 1/2 contain the current exact campaign
• 221 tests and typecheck pass
• evidence validation passes
• coverage remains humanEvidence 0, a11y-at-tested 0, a11y-user-validated 0, with all 26 human requirements missing

This changes coordination state only. It creates no assistive-technology evidence, disabled-user validation, conformance claim, certification, or whole-product accessibility claim.