docs: archive relay.ngit.dev migration materials for reference

Move migration guide and scripts to docs/archive/2026-01-relay-ngit-dev-migration/
with clear warnings that these are reference-only materials from a specific
migration context, not general-purpose tools.

These materials document the relay.ngit.dev migration from ngit-relay to
ngit-grasp in January 2026. The scripts were developed iteratively during
the migration and are specific to that context. They are preserved for:
- Historical reference
- Context for production fixes in this branch
- Inspiration for future migrations (not direct reuse)

The migration uncovered critical bugs now fixed in this branch:
- Git protocol error handling
- Naughty list false positives
- Purgatory event tracking
- Sync startup issues
- Configuration management

docs/archive/2026-01-relay-ngit-dev-migration/README.md

@@ -0,0 +1,61 @@
+# relay.ngit.dev Migration Archive (January 2026)
+
+**Status:** Reference only - not maintained
+
+This directory contains the migration guide and scripts used during the 
+relay.ngit.dev migration from ngit-relay to ngit-grasp in January 2026.
+
+## ⚠️ Important
+
+These materials are **archived for reference only**:
+
+- **Scripts are specific to the relay.ngit.dev migration context**
+- **Not designed for general use or other migrations**
+- **May not work without modification**
+- **Not maintained or supported**
+
+Do not expect these scripts to work out of the box for your migration.
+
+## What's Here
+
+- `migration-guide.md` - Lessons learned, approach, and context from the actual migration
+- `scripts/` - Analysis and validation scripts used during the migration process
+
+## Why Archive This?
+
+The relay.ngit.dev migration uncovered numerous bugs and edge cases that resulted 
+in critical production fixes. See commits in the `4bc5-relay-ngit-dev-migration-v2` 
+branch for details.
+
+These materials document:
+
+- Real-world migration challenges encountered
+- Debugging approaches that worked in practice
+- Context for production fixes merged from this branch
+- Iterative script development during active migration
+
+## Using This as Reference
+
+If you're planning a migration to ngit-grasp:
+
+1. **Read the migration guide** for conceptual approach and lessons learned
+2. **Review the scripts** to understand what kinds of analysis were needed
+3. **Expect to write your own scripts** tailored to your specific context
+4. **Test extensively** in a non-production environment first
+
+These materials show what was needed for one specific migration, not a 
+general-purpose migration toolkit.
+
+## Context
+
+This migration was completed in January 2026 and resulted in relay.ngit.dev 
+running ngit-grasp in production. The branch containing these materials also 
+includes critical fixes for:
+
+- Git protocol error handling
+- Naughty list false positives
+- Purgatory event tracking
+- Sync startup issues
+- Configuration management
+
+Those fixes are now part of the main codebase.

docs/how-to/README.md

@@ -110,18 +110,6 @@ How-to guides are **recipes** that show you how to solve specific problems or ac
 
 ---
 
-### [Migrate to ngit-grasp](migrate-to-ngit-grasp.md)
-**Status:** ✅ Available
-
-**Problem:** Switch from another GRASP implementation  
-**You'll learn:**
-- Analyze existing relay data
-- Identify repositories needing attention
-- Run migration analysis scripts
-- Plan and execute cutover
-
----
-
 ## How to Use How-To Guides
 
 1. **Find your problem** - Browse or search for what you need