chore: archive legacy Identity, Workday, and Intune folders

- Move Identity/, Workday/, Intune/ to archive/ (superseded by nexus-mcp shards)
- Move 'Local Setup.md' to archive/ (superseded by nexus-mcp/Local-Setup.md)
- Add archive/README.md explaining migration and preserved content
- Clean repository structure: only nexus-mcp, documentation, and .github remain active

All legacy functionality migrated to nexus-mcp sharded architecture.
Archived folders preserved for reference and historical context.

Refs: SESSION_SNAPSHOT_2026-04-13.md

archive/README.md

@@ -0,0 +1,48 @@
+# Archive — Legacy MCP Servers
+
+This folder contains the original Identity and Workday MCP server implementations that were migrated into the unified Nexus-MCP sharded architecture on 2026-04-13.
+
+## Archived folders
+
+### Identity/
+- **Original purpose:** Active Directory MCP server with 8 tools
+- **Key files:** `identity_mcp_server.py`, `ad_adapter.py`, `identity_backend.py`
+- **Status:** Superseded by `nexus-mcp/src/shards/identity.py`
+- **Preserved for:** Reference implementation, PowerShell adapter patterns
+
+### Workday/
+- **Original purpose:** Workday HCM MCP server with worker lookup and drift detection
+- **Key files:** `server.py`, `lib/data.py`, mismatch scan functions
+- **Status:** Superseded by `nexus-mcp/src/shards/workday.py` and `nexus-mcp/src/shards/audit.py`
+- **Preserved for:** Mock data structures, drift scan algorithms
+
+### Local Setup.md
+- **Original purpose:** Installation guide for the monolithic Identity server
+- **Status:** Replaced by `nexus-mcp/Local-Setup.md`
+
+## Migration summary
+
+**Migration date:** 2026-04-13  
+**Commit:** feat(nexus): implement sharded architecture  
+**Session snapshot:** [documentation/project-history/SESSION_SNAPSHOT_2026-04-13.md](../documentation/project-history/SESSION_SNAPSHOT_2026-04-13.md)
+
+**What was migrated:**
+- 8 Identity tools → `nexus-mcp/src/shards/identity.py` (15 tools including Entra)
+- 3 Workday worker tools → `nexus-mcp/src/shards/workday.py`
+- 5 drift detection tools → `nexus-mcp/src/shards/audit.py`
+- AD PowerShell adapter → `nexus-mcp/lib/ad_adapter.py`
+- Mock data → `nexus-mcp/lib/mock_data.py`
+- Test suites → `nexus-mcp/tests/identity_tests/` and `nexus-mcp/tests/workday_tests/`
+
+## Active server
+
+**Current primary:** [nexus-mcp/](../nexus-mcp/)
+
+For installation, configuration, and usage, see:
+- [nexus-mcp/README.md](../nexus-mcp/README.md) — full tool reference
+- [nexus-mcp/Local-Setup.md](../nexus-mcp/Local-Setup.md) — installation guide
+- [README.md](../README.md) — repository status page
+
+---
+
+**Note:** These folders are preserved for reference and historical context. Do not use them for new development. All active work should occur in `nexus-mcp/`.