Add _graph extension support to Neo4j driver

- Implement TraverseFollows using Cypher path queries on FOLLOWS relationships
- Implement TraverseFollowers using reverse path traversal
- Implement FindMentions using MENTIONS relationships from p-tags
- Implement TraverseThread using REFERENCES relationships from e-tags
  with bidirectional traversal (inbound replies, outbound parents)
- Add GraphAdapter to bridge Neo4j to graph.GraphDatabase interface
- Add GraphResult type implementing graph.GraphResultI for Neo4j
- Initialize graph executor for Neo4j backend in app/main.go

The implementation uses existing Neo4j schema and relationships created
by SaveEvent() - no schema changes required. The _graph extension now
works transparently with either Badger or Neo4j backends.

Bump version to v0.35.0

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

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

pkg/neo4j/graph-mentions.go

@@ -0,0 +1,143 @@
+package neo4j
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"git.mleku.dev/mleku/nostr/encoders/hex"
+	"next.orly.dev/pkg/protocol/graph"
+)
+
+// FindMentions finds events that mention a pubkey via p-tags.
+// This returns events grouped by depth, where depth represents how the events relate:
+//   - Depth 1: Events that directly mention the seed pubkey
+//   - Depth 2+: Not typically used for mentions (reserved for future expansion)
+//
+// The kinds parameter filters which event kinds to include (e.g., [1] for notes only,
+// [1,7] for notes and reactions, etc.)
+//
+// Uses Neo4j MENTIONS relationships created by SaveEvent when processing p-tags.
+func (n *N) FindMentions(pubkey []byte, kinds []uint16) (graph.GraphResultI, error) {
+	result := NewGraphResult()
+
+	if len(pubkey) != 32 {
+		return result, fmt.Errorf("invalid pubkey length: expected 32, got %d", len(pubkey))
+	}
+
+	pubkeyHex := strings.ToLower(hex.Enc(pubkey))
+	ctx := context.Background()
+
+	// Build kinds filter if specified
+	var kindsFilter string
+	params := map[string]any{
+		"pubkey": pubkeyHex,
+	}
+
+	if len(kinds) > 0 {
+		// Convert uint16 slice to int64 slice for Neo4j
+		kindsInt := make([]int64, len(kinds))
+		for i, k := range kinds {
+			kindsInt[i] = int64(k)
+		}
+		params["kinds"] = kindsInt
+		kindsFilter = "AND e.kind IN $kinds"
+	}
+
+	// Query for events that mention this pubkey
+	// The MENTIONS relationship is created by SaveEvent when processing p-tags
+	cypher := fmt.Sprintf(`
+		MATCH (e:Event)-[:MENTIONS]->(u:NostrUser {pubkey: $pubkey})
+		WHERE true %s
+		RETURN e.id AS event_id
+		ORDER BY e.created_at DESC
+	`, kindsFilter)
+
+	queryResult, err := n.ExecuteRead(ctx, cypher, params)
+	if err != nil {
+		return result, fmt.Errorf("failed to query mentions: %w", err)
+	}
+
+	// Add all found events at depth 1
+	for queryResult.Next(ctx) {
+		record := queryResult.Record()
+		eventID, ok := record.Values[0].(string)
+		if !ok || eventID == "" {
+			continue
+		}
+
+		// Normalize to lowercase for consistency
+		eventID = strings.ToLower(eventID)
+		result.AddEventAtDepth(eventID, 1)
+	}
+
+	n.Logger.Debugf("FindMentions: found %d events mentioning pubkey %s", result.TotalEvents, safePrefix(pubkeyHex, 16))
+
+	return result, nil
+}
+
+// FindMentionsFromHex is a convenience wrapper that accepts hex-encoded pubkey.
+func (n *N) FindMentionsFromHex(pubkeyHex string, kinds []uint16) (*GraphResult, error) {
+	pubkey, err := hex.Dec(pubkeyHex)
+	if err != nil {
+		return nil, err
+	}
+	result, err := n.FindMentions(pubkey, kinds)
+	if err != nil {
+		return nil, err
+	}
+	return result.(*GraphResult), nil
+}
+
+// FindMentionsByPubkeys returns events that mention any of the given pubkeys.
+// Useful for finding mentions across a set of followed accounts.
+func (n *N) FindMentionsByPubkeys(pubkeys []string, kinds []uint16) (*GraphResult, error) {
+	result := NewGraphResult()
+
+	if len(pubkeys) == 0 {
+		return result, nil
+	}
+
+	ctx := context.Background()
+
+	// Build kinds filter if specified
+	var kindsFilter string
+	params := map[string]any{
+		"pubkeys": pubkeys,
+	}
+
+	if len(kinds) > 0 {
+		kindsInt := make([]int64, len(kinds))
+		for i, k := range kinds {
+			kindsInt[i] = int64(k)
+		}
+		params["kinds"] = kindsInt
+		kindsFilter = "AND e.kind IN $kinds"
+	}
+
+	// Query for events that mention any of the pubkeys
+	cypher := fmt.Sprintf(`
+		MATCH (e:Event)-[:MENTIONS]->(u:NostrUser)
+		WHERE u.pubkey IN $pubkeys %s
+		RETURN DISTINCT e.id AS event_id
+		ORDER BY e.created_at DESC
+	`, kindsFilter)
+
+	queryResult, err := n.ExecuteRead(ctx, cypher, params)
+	if err != nil {
+		return result, fmt.Errorf("failed to query mentions: %w", err)
+	}
+
+	for queryResult.Next(ctx) {
+		record := queryResult.Record()
+		eventID, ok := record.Values[0].(string)
+		if !ok || eventID == "" {
+			continue
+		}
+
+		eventID = strings.ToLower(eventID)
+		result.AddEventAtDepth(eventID, 1)
+	}
+
+	return result, nil
+}