Prepare Scriptorium Public Alpha

[foxsplendid]

What changed

• Make Windows path selection explicit and fail closed on conflicting or invalid environment roots.
• Keep missing Agent homes actionable without creating directories or reporting internal errors.
• Pin CI dependencies to sanitized component commits and Node 24-compatible Actions.
• Add an honest Public Alpha case study, synthetic demo poster, evidence snapshots, and limitations.
• Make the canonical Codex adapter test independent of the runner's local Agent home.

Why

This turns the suite entry point into a reproducible, privacy-bounded release candidate for AI4Science researchers on Windows.

Validation

• 212 tests: 206 passed, 6 skipped in an isolated empty-profile environment.
• Synthetic nine-stage golden demo passed with six assertions.
• JSON/SVG, Markdown-link, evidence-hash, privacy, credential, and public-history audits passed.
• GitHub Actions push run 29818931932 and PR run 29818934741 passed on commit 8069cbf, including Windows 3.11/3.12, Ubuntu 3.11/3.12, and the cross-repository Windows E2E.