* feat(web): add topic pages and reply threads (Phase 4 M5) - Topic detail page at /t/{slug}/{rkey} with JSON-LD DiscussionForumPosting - TopicView component with markdown content, author, category, tags, stats - ReplyCard with depth-based indentation and anchor links (#post-{n}) - ReplyThread with paginated reply list and empty state - MarkdownContent renderer with DOMPurify XSS sanitization - Slug utility for SEO-friendly topic URLs - API client: getTopicByRkey, mock reply data, MSW handlers - Breadcrumbs updated to support optional href (current page) * fix(ci): update pnpm version from 9 to 10 to match local pnpm 10 auto-generates pnpm-workspace.yaml with ignoredBuiltDependencies which lacks the packages field required by pnpm 9, causing CI failures.