Clarify IRW case-study access and correct sharing preview

[Tyler-Windes]

Changes

• Keep the Confluence destination unchanged and label it "sign-in required".
• Use a distinct IRW sharing card with matching OG/Twitter metadata on the canonical and legacy IRW routes. Preserve the original Workflow Intake image.
• Extend the existing explicit validator for the new asset, actual dimensions, matching metadata and sign-in label.

Validation and limits

• Existing local public-site validation: 119/119 checks passed; independent readback matched all 32 input bindings and 13 build entries.
• Exact four-file diff reviewed; no CSS, homepage, workflow, permission or unrelated project changes.
• Production browser access was denied by enforced policy before rendering. No screenshots, desktop/mobile, keyboard, console or rendered redirect pass is claimed.

Follows already merged PR #1 at 9c011c3 under the owner's publish-first authorization. Existing GitHub Pages workflow is unchanged.