imageTextBlock: optional square image + host subheading fields

Deferred from PR #4760 (AI for Business Leaders event page), host (Mike Smedley) section, as a separate PBI because these are new reusable component capabilities that should be designed properly rather than added ad hoc. Design feedback from Tiago.

1. Square host photo (#13) — images render via components/blocks/imageComponents/ImageComponentLayout.tsx (w-full rounded-md). Adding aspect-square there would square every image site-wide (not acceptable). Add an optional boolean to the mediaConfiguration Tina schema (e.g. squareImage) and conditionally apply aspect-square object-cover, set only on host/profile blocks. Decision: square (1:1) vs another portrait ratio.

2. Host title styling (#14) — the host block is a generic imageTextBlock; the role line ("SSW · AI Engagement Lead · Melbourne") is just the first paragraph of description and renders as plain body text. Add an optional subheading field to the imageTextBlock schema, rendered with distinct styling (e.g. text-sswRed font-semibold uppercase tracking-wide), and move the role line into it.

Note: both add Tina schema fields, so tina/tina-lock.json must be regenerated (run pnpm dev to refresh it) and TinaCloud re-indexed, or the build fails on a schema mismatch.

Acceptance: new fields appear in the Tina editor, round-trip, and render; lockfile regenerates; applied to the host block on the event page.

Refs: PR #4760, Tiago design feedback items #13, #14.

Start with components/blocks/imageComponents/ImageComponentLayout.tsx and locate the Tina schema for imageTextBlock and mediaConfiguration. Check how the host block is represented on the event page, then verify the new fields appear in Tina, round-trip, and render correctly. Run pnpm dev to regenerate tina/tina-lock.json and confirm the schema mismatch is resolved.