Export (export.rs): ZIP archive with auto-chunking at 4GB. Four scopes:
identity only, posts only, posts+identity, everything (posts+key+follows+
profiles+settings). Includes blobs. Manifest JSON tracks metadata.
Import (import.rs): Read ZIP summary without importing (preview).
Import public posts into current identity with new PostIds + original
timestamps. Import as new identity (creates identity subdir from key).
Uses spawn_blocking for ZIP I/O to avoid Send issues with ZipArchive.
Tauri IPC: export_data, import_summary, import_public_posts,
import_as_new_identity commands. IdentityManager.base_dir() getter.
Frontend: Export wizard lightbox with scope radio buttons + output dir.
Import wizard with ZIP path, preview summary, action selection.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>