Add public changelog with Atom feed and What's New indicator

- Changelog entries authored as markdown files in apps/journal/changelog/
  with YAML frontmatter, loaded via Vite import.meta.glob at build time
- /changelog list page with date, title, and preview
- /changelog/:slug detail page with full markdown rendering (react-markdown)
  and Open Graph meta tags for social sharing
- /changelog/feed.xml Atom feed with auto-discovery <link> tags
- "What's New" dot on nav bar using localStorage timestamp tracking
- Notification toggle: users can permanently disable/re-enable the indicator
- i18n strings for en and de
- Initial changelog entry covering the Phase 1 launch

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openspec/changes/changelog/proposal.md

@@ -22,7 +22,7 @@ project is alive and improving), and social followers (shareable updates).
 
 ### New Capabilities
 
-- `changelog`: Public changelog with dated entries, shareable individual pages with OG tags, "what's new" indicator
+- `changelog`: Public changelog with dated entries, shareable individual pages with OG tags, "what's new" indicator, RSS/Atom feed
 
 ### Modified Capabilities
 
@@ -30,8 +30,8 @@ project is alive and improving), and social followers (shareable updates).
 
 ## Impact
 
-- **Files**: New routes (`/changelog`, `/changelog/:slug`), markdown entry files
-  in `docs/changelog/` or `apps/journal/changelog/`, nav bar update
+- **Files**: New routes (`/changelog`, `/changelog/:slug`, `/changelog/feed.xml`),
+  markdown entry files in `apps/journal/changelog/`, nav bar update
 - **Dependencies**: A markdown renderer (could reuse `react-markdown` or render
   at build time)
 - **i18n**: Changelog entries written in English (primary audience), German