Implement Tag-based e/p model for Neo4j backend (v0.36.0)

- Add unified Tag-based model where e/p tags create intermediate Tag nodes
  with REFERENCES relationships to Event/NostrUser nodes
- Update save-event.go: addPTagsInBatches and addETagsInBatches now create
  Tag nodes with TAGGED_WITH and REFERENCES relationships
- Update delete.go: CheckForDeleted uses Tag traversal for kind 5 detection
- Add v3 migration in migrations.go to convert existing direct REFERENCES
  and MENTIONS relationships to the new Tag-based model
- Create comprehensive test file tag_model_test.go with 15+ test functions
  covering Tag model, filter queries, migrations, and deletion detection
- Update save-event_test.go to verify new Tag-based relationship patterns
- Update WOT_SPEC.md with Tag-Based References documentation section
- Update CLAUDE.md and README.md with Neo4j Tag-based model documentation
- Bump version to v0.36.0

This change enables #e and #p filter queries to work correctly by storing
all tags (including e/p) through intermediate Tag nodes.

Files modified:
- pkg/neo4j/save-event.go: Tag-based e/p relationship creation
- pkg/neo4j/delete.go: Tag traversal for deletion detection
- pkg/neo4j/migrations.go: v3 migration for existing data
- pkg/neo4j/tag_model_test.go: New comprehensive test file
- pkg/neo4j/save-event_test.go: Updated for new model
- pkg/neo4j/WOT_SPEC.md: Tag-Based References documentation
- pkg/neo4j/README.md: Architecture and example queries
- CLAUDE.md: Repository documentation update
- pkg/version/version: Bump to v0.36.0

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/version/version

@@ -1 +1 @@
-v0.35.5
+v0.36.0