Add BBolt database backend for HDD-optimized archival relays (v0.48.0)

- BBolt B+tree backend with sequential access patterns for spinning disks
- Write batching (5000 events / 128MB / 30s flush) to reduce disk thrashing
- Adjacency list storage for graph data (one key per vertex, not per edge)
- Bloom filter for fast negative edge existence checks (~12MB for 10M edges)
- No query cache (saves RAM, B+tree reads are fast enough on HDD)
- Migration tool: orly migrate --from badger --to bbolt
- Configuration: ORLY_BBOLT_* environment variables

Files modified:
- app/config/config.go: Added BBolt configuration options
- main.go: Added migrate subcommand and BBolt config wiring
- pkg/database/factory.go: Added BBolt factory registration
- pkg/bbolt/*: New BBolt database backend implementation

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

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

pkg/bbolt/markers.go

@@ -0,0 +1,62 @@
+//go:build !(js && wasm)
+
+package bbolt
+
+import (
+	bolt "go.etcd.io/bbolt"
+)
+
+const markerPrefix = "marker:"
+
+// SetMarker sets a metadata marker.
+func (b *B) SetMarker(key string, value []byte) error {
+	return b.db.Update(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(bucketMeta)
+		if bucket == nil {
+			return nil
+		}
+		return bucket.Put([]byte(markerPrefix+key), value)
+	})
+}
+
+// GetMarker gets a metadata marker.
+func (b *B) GetMarker(key string) (value []byte, err error) {
+	err = b.db.View(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(bucketMeta)
+		if bucket == nil {
+			return nil
+		}
+		data := bucket.Get([]byte(markerPrefix + key))
+		if data != nil {
+			value = make([]byte, len(data))
+			copy(value, data)
+		}
+		return nil
+	})
+	return
+}
+
+// HasMarker checks if a marker exists.
+func (b *B) HasMarker(key string) bool {
+	var exists bool
+	b.db.View(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(bucketMeta)
+		if bucket == nil {
+			return nil
+		}
+		exists = bucket.Get([]byte(markerPrefix+key)) != nil
+		return nil
+	})
+	return exists
+}
+
+// DeleteMarker deletes a marker.
+func (b *B) DeleteMarker(key string) error {
+	return b.db.Update(func(tx *bolt.Tx) error {
+		bucket := tx.Bucket(bucketMeta)
+		if bucket == nil {
+			return nil
+		}
+		return bucket.Delete([]byte(markerPrefix + key))
+	})
+}