chore: archive v2.3 milestone files

Archive setup sharing, currency system, and i18n foundation milestone.
Reorganize ROADMAP.md with v2.3 details block, update PROJECT.md,
MILESTONES.md, STATE.md deferred items, and RETROSPECTIVE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/MILESTONES.md

@@ -1,5 +1,26 @@
 # Milestones
 
+## v2.3 Global & Social Ready (Shipped: 2026-04-19)
+
+**Phases completed:** 3 phases (32-34), 18 plans
+**Timeline:** 6 days (2026-04-13 → 2026-04-19)
+**Codebase:** 217 files changed (+24,291 / -991), 99 commits
+
+**Key accomplishments:**
+
+- Setup visibility system: isPublic replaced with private/link/public visibility column, shares table with 128-bit token entropy, visibility-transition side effects (deactivate/reactivate links)
+- ShareModal with Google Docs-style UX: visibility picker, share link creation with expiry, active links list with revoke, deactivation warning
+- Shared setup viewer: `/s/:token` short URL redirect, `/api/shared/:token` public endpoint, read-only mode with owner controls gated, inline "Shared setup" banner
+- Multi-currency foundation: market_prices + community_prices tables, ECB exchange rates via frankfurter.app with 24h cache, currency conversion service
+- Community price aggregation: ownership-validated submissions, PERCENTILE_CONT(0.5) median with 3-report minimum, market-aware MSRP on catalog detail pages
+- i18n framework: react-i18next + 6 namespaces (common/collection/threads/setups/onboarding/settings/catalog), English + German locales, language picker in settings, locale-aware formatting
+
+**Known deferred items at close:** 6 (see STATE.md Deferred Items)
+
+**Archive:** `.planning/milestones/v2.3-ROADMAP.md`, `.planning/milestones/v2.3-REQUIREMENTS.md`
+
+---
+
 ## v2.2 User Experience Polish (Shipped: 2026-04-13)
 
 **Phases completed:** 36 phases, 68 plans, 120 tasks