Public Changelog & Content System

This release introduces a complete public changelog system with CardStack animations, modernized content pages, and comprehensive test coverage.

Public changelog system - Full timeline UI with MDX-based content and draft/published support
Typed detail routes - Click changelog items to open their detail page, direct URLs still work
CardStack widget - Animated changelog cards in organization sidebar with dismiss functionality
Local dismissal state - Per-browser changelog dismissal persistence with localStorage
Debug Panel - Development-only panel with "Reset Changelog" and other debug actions
Active navigation highlighting - Header navigation now shows which section you're in
Blog posts section - Sample blog content with authentication, Stripe, Prisma, Next.js, and TailwindCSS guides

Modernized changelog timeline - Clean vertical line design with dot markers and compact cards
Content header component - Reusable header with title, description, and navigation tabs
Docs moved to (layout) route group - Better organization of public content routes
Post card variants - Multiple display variants for blog post cards

Changelog reset - Debug panel action clears local changelog dismissals during development
E2E test stability - Handle session invalidation and correct selectors for sign out flow

Focused unit tests - changelog-manager coverage for parsing, sorting, draft filtering, and slug lookup
3 new E2E tests - Timeline rendering, item navigation, and direct URL access
All tests passing with zero skipped