Implement BBolt ImportEventsFromReader for migration (v0.48.1)

- Add import-export.go with full JSONL import support for bbolt
- Remove Import/Export/ImportEventsFromReader stubs from stubs.go
- Includes batched write flush after import completion
- Progress logging every 5 seconds during import

Files modified:
- pkg/bbolt/import-export.go: New file with import functionality
- pkg/bbolt/stubs.go: Remove implemented stubs
- pkg/version/version: v0.48.0 -> v0.48.1

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

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

pkg/bbolt/stubs.go

@@ -5,7 +5,6 @@ package bbolt
 import (
 	"context"
 	"errors"
-	"io"
 	"time"
 
 	"next.orly.dev/pkg/database"
@@ -94,30 +93,6 @@ func (b *B) CheckForDeleted(ev *event.E, admins [][]byte) error {
 	return nil // Not deleted by default
 }
 
-// Import imports events from a reader.
-func (b *B) Import(rr io.Reader) {
-	// TODO: Implement
-}
-
-// Export exports events to a writer.
-func (b *B) Export(c context.Context, w io.Writer, pubkeys ...[]byte) {
-	// TODO: Implement
-}
-
-// ImportEventsFromReader imports events from a JSONL reader.
-func (b *B) ImportEventsFromReader(ctx context.Context, rr io.Reader) error {
-	return errNotImplemented
-}
-
-// ImportEventsFromStrings imports events from JSON strings.
-func (b *B) ImportEventsFromStrings(ctx context.Context, eventJSONs []string, policyManager interface {
-	CheckPolicy(action string, ev *event.E, pubkey []byte, remote string) (bool, error)
-}) error {
-	return errNotImplemented
-}
-
-
-
 // GetSubscription gets a user's subscription.
 func (b *B) GetSubscription(pubkey []byte) (*database.Subscription, error) {
 	return nil, errNotImplemented