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- Historical reference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

1 files changed, 0 insertions, 12 deletions

diff --git a/docs/how-to/README.md b/docs/how-to/README.md
index f755be1..087ae53 100644
--- a/docs/how-to/README.md
+++ b/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