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/RETROSPECTIVE.md

@@ -2,6 +2,49 @@
 
 *A living document updated after each milestone. Lessons feed forward into future planning.*
 
+## Milestone: v2.3 — Global & Social Ready
+
+**Shipped:** 2026-04-19
+**Phases:** 3 (32-34) | **Plans:** 18 | **Commits:** 99
+
+### What Was Built
+- Setup visibility system replacing boolean isPublic with private/link/public, share tokens with 128-bit entropy, and visibility-transition side effects
+- ShareModal with Google Docs-style UX — visibility picker, link creation/expiry, revoke, deactivation warning
+- Shared setup viewer with short URL redirect, read-only mode, and three-way data source logic
+- Multi-currency pricing: ECB exchange rates with 24h cache, market_prices and community_prices tables, ownership-validated submissions, median aggregation
+- Market-aware MSRP on catalog detail pages with collapsible "Other Markets" section
+- i18n framework: react-i18next, 7 namespaces, English + German translations, language detection, language picker
+
+### What Worked
+- Phased schema approach: do the migration first (32-01), service layer next, UI last — no mid-phase schema surprises
+- Dynamic import to break circular dependency (setup.service.ts → share.service.ts) was clean and discovered quickly
+- ECB exchange rate module-level cache is dead simple and effective for a single-process Bun app
+- Namespace-per-feature for i18n matches the existing file-based routing structure naturally
+
+### What Was Inefficient
+- Phase 32 progress table in ROADMAP.md showed 0/4 Planned despite all plans being complete — tracking drift not caught until milestone close
+- Several todos from early in the milestone (April 10) accumulated and weren't cleared before close — 6 deferred items
+- REQUIREMENTS.md was never refreshed for v2.2 or v2.3; requirements were tracked informally in STATE.md decisions
+
+### Patterns Established
+- `visibility` text enum over boolean flags for any future toggle-able states (shareable, public, featured)
+- Shares as a separate table with revocation semantics — reusable pattern for future permission systems
+- Community aggregation floor (3 reports minimum) before surfacing median — prevents single-user stat manipulation
+- i18n namespace per feature domain matches the codebase's existing routing and component organization
+
+### Key Lessons
+1. Keep REQUIREMENTS.md current across milestones — informal tracking in STATE.md decisions is not a substitute
+2. Todo triage at milestone close works, but earlier triage (mid-milestone) would reduce the deferred backlog
+3. The shares deactivate/reactivate pattern (not destroy) gives users a better experience at near-zero complexity cost
+4. Language detection: localStorage-first is the right call — user preference must win over browser default
+
+### Cost Observations
+- Model mix: sonnet throughout
+- Sessions: ~18 plan executions across 6 days
+- Notable: Phase 34 (i18n) was the heaviest at 8 plans — string extraction across the full app touches every component
+
+---
+
 ## Milestone: v1.0 — MVP
 
 **Shipped:** 2026-03-15