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/v2.3-REQUIREMENTS.md

@@ -0,0 +1,78 @@
+# Requirements Archive: GearBox v2.3 Global & Social Ready
+
+**Archived:** 2026-04-19
+**Milestone shipped:** v2.3
+
+> Note: The active REQUIREMENTS.md at close was scoped to v2.1 Public Discovery requirements (all complete).
+> v2.3-specific requirements (sharing, currency, i18n) were tracked as decisions in STATE.md and active items in PROJECT.md.
+
+---
+
+# Requirements: GearBox v2.1 Public Discovery
+
+**Defined:** 2026-04-09
+**Core Value:** Help people make better gear decisions — discover what others use, compare real-world data, and see how a potential buy affects your setup before committing.
+
+## v2.1 Requirements
+
+### Public Access
+
+- [x] **PUBL-01**: User can browse the global item catalog without logging in
+- [x] **PUBL-02**: User can view public setups without logging in
+- [x] **PUBL-03**: User can view user profiles without logging in
+- [x] **PUBL-04**: Anonymous visitors see the landing page without auth spinner or redirect
+- [x] **PUBL-05**: Login is only required when user attempts to create/edit/delete their own data
+
+### Discovery
+
+- [x] **DISC-01**: Landing page displays an always-visible catalog search bar at the top
+- [x] **DISC-02**: Landing page shows a feed of popular setups below the search
+- [x] **DISC-03**: Landing page shows recently added catalog items
+- [x] **DISC-04**: Landing page shows trending categories
+- [x] **DISC-05**: Authenticated users see a "Go to Collection" entry point from the landing page
+
+### Catalog Enrichment
+
+- [x] **CATL-01**: Global items have attribution fields (sourceUrl, manufacturer, imageCredit, imageSourceUrl)
+- [x] **CATL-02**: Global items have a unique constraint on (brand, model) preventing duplicates
+- [x] **CATL-03**: Catalog detail pages display image attribution with credit and source link
+- [x] **CATL-04**: Bulk import API endpoint accepts multiple catalog items in one request
+- [x] **CATL-05**: Bulk import uses upsert semantics (ON CONFLICT update, not fail)
+
+### Agent Seeding Tools
+
+- [x] **SEED-01**: MCP server has a dedicated `upsert_catalog_item` tool that writes to globalItems (not user-scoped)
+- [x] **SEED-02**: MCP server has a `bulk_upsert_catalog` tool for batch catalog population
+- [x] **SEED-03**: Catalog MCP tools include attribution fields (sourceUrl, manufacturer, imageCredit) as parameters
+
+### Infrastructure
+
+- [x] **INFR-01**: Public API endpoints are rate-limited to prevent abuse
+- [x] **INFR-02**: Discovery feed endpoint uses cursor pagination for scalability
+
+## Traceability
+
+| Requirement | Phase | Status |
+|-------------|-------|--------|
+| PUBL-01 | Phase 24 | Complete |
+| PUBL-02 | Phase 24 | Complete |
+| PUBL-03 | Phase 24 | Complete |
+| PUBL-04 | Phase 24 | Complete |
+| PUBL-05 | Phase 24 | Complete |
+| INFR-01 | Phase 24 | Complete |
+| CATL-01 | Phase 25 | Complete |
+| CATL-02 | Phase 25 | Complete |
+| CATL-03 | Phase 25 | Complete |
+| CATL-04 | Phase 25 | Complete |
+| CATL-05 | Phase 25 | Complete |
+| SEED-01 | Phase 25 | Complete |
+| SEED-02 | Phase 25 | Complete |
+| SEED-03 | Phase 25 | Complete |
+| DISC-01 | Phase 26 | Complete |
+| DISC-02 | Phase 26 | Complete |
+| DISC-03 | Phase 26 | Complete |
+| DISC-04 | Phase 26 | Complete |
+| DISC-05 | Phase 26 | Complete |
+| INFR-02 | Phase 26 | Complete |
+
+**Coverage:** 20/20 v2.1 requirements complete.