fix(end-page): align thank-you paragraph typography with other admin content

[tutntut]

Closes #9434

Problem

Markdown bullet points added to the thank-you page paragraph render with visibly different styling from the surrounding text — the paragraph text appears bolded while the bullets do not. Closes #9434.

Solution

The bolded bullets were a symptom, not the bug: the end page styled its admin-authored paragraph with subhead-1 (weight 500, secondary.500), while every other renderer of primary admin-authored paragraph content — FormInstructions, SectionField, ParagraphField — uses body-1 (weight 400, secondary.700). A survey of all 15 useMdComponents consumers confirmed the end page was the sole outlier. Switching EndPageBlock to the shared baseline fixes both plain paragraphs and bullet lists in one move. A Storybook story with a bulleted paragraph was added as a repro.

Alternatives considered

• We first tried adding a list-style fallback inside the shared useMdComponents hook so ul elements would pick up the caller's text style, but dropped it — it only patched bullets, leaving plain end-page paragraphs still rendered at weight 500, and it added complexity to a shared hook to work around one caller's styling choice.
• We tried to trace why the end page originally used subhead-1, but the git history is flattened at the monorepo migration, so the original intent is unrecoverable. It likely aimed to make the thank-you message read as a subtitle under the h2 title — fine for one-liners, but it breaks down for multi-paragraph admin content with lists.

Screenshots

Story	Before	After
End page with bullets
End page default

Breaking Changes

No - backwards compatible. Note the visual change applies to every form's thank-you page (paragraph weight 500 → 400, colour secondary.500 → secondary.700) — worth a design sanity-check.

Tests

TC1: bulleted thank-you paragraph

• Create a form; in the thank-you page settings, set a paragraph containing markdown bullets (* item)
• Submit the form
• Verify the intro text and the bullet items render at the same weight/colour, matching a paragraph field's styling

TC2: existing plain thank-you paragraphs

• Open any form with a plain (non-bulleted) thank-you paragraph and submit
• Verify the paragraph renders like other admin-authored body text (no bolding), and the title/Response ID area is unchanged

Clean-up

• Close fix(end-page): align thank-you paragraph typography with other admin content #9756

🤖 Generated with Claude Code

[tutntut]

Why the fix is here rather than in the shared useMdComponents hook: the reported "bolded bullets" were a symptom, not the bug. EndPageBlock styled its admin-authored paragraph with subhead-1 (weight 500, secondary.500), while every other renderer of primary admin-authored paragraph content — FormInstructions, SectionField, ParagraphField — uses body-1 (weight 400, secondary.700). A survey of all 15 useMdComponents consumers confirmed EndPageBlock was the sole outlier among primary-paragraph renderers (ImageField and FormLabel deviate deliberately, as smaller supporting text). Changing the end-page text style to the shared baseline fixes bullets and plain paragraphs in one move.

Alternatives tried and rejected:

• A listStyles fallback in useMdComponents so ul picks up styles.text — only patched bullets, left plain paragraphs at weight 500, and added complexity to a shared hook to work around one caller. This was the first implementation attempt and was reverted.
• Passing explicit list styles from EndPageBlock only — same partial-fix problem.