Merge relay.ngit.dev migration: bug fixes and migration tooling

This merge includes critical bug fixes and comprehensive migration tooling
developed during the relay.ngit.dev migration effort.

Bug Fixes:
- Fix git protocol error handling to return HTTP 200 with ERR pkt-line
- Fix naughty list false positives and DNS failure identification
- Fix database query filters in load_existing_events (remove .since())
- Fix OID fetch tracking to distinguish 0 OIDs from successful fetches
- Fix purgatory event source tracking for filtered expiry logging
- Implement OID retry logic for 'not our ref' errors

Migration Tools & Documentation:
- Complete 5-phase migration analysis pipeline with orchestration script
- Phase 1: Event fetching from source relay
- Phase 2: Git sync verification
- Phase 3: Categorization and relay comparison
- Phase 4: Log extraction (parse failures, purgatory expiry)
- Phase 5: Action classification for migration decisions
- Comprehensive migration guide with lessons learned
- Troubleshooting guide for permission and corruption issues

Configuration:
- Add NGIT_LOG_LEVEL configuration option
- Update git throttle limits to 60/minute
- Improve logging throughout for better observability

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+# 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.