Extend the wiki's RichTextEditor to the Posts editor and close the
stored-XSS gap on public post bodies.
- RichTextEditor: add `variant` prop — `full` (wiki), `post` (no
internal wiki-page link picker), `minimal` (image-only, for
Screenshots captions). Toolbar sections rendered conditionally.
- PostEditor: replace the body textarea with a lazy-loaded
RichTextEditor in Suspense; variant chosen by category
(minimal for screenshots, post otherwise).
- posts.model: sanitize body via shared cleanBody on create/update,
treat an empty TipTap `<p></p>` as null, and auto-derive the
excerpt from the body (max 280 chars) when left blank.
- sanitizeHtml util: add deriveExcerpt() helper.
- FiveOnFriday / NewsletterIssue: wrap dangerouslySetInnerHTML with
DOMPurify.sanitize() as defense-in-depth on render.
No schema or dependency changes. Verified end-to-end against the
local stack: 24/24 API assertions and a full UI round-trip across
all four post categories.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
