RustBox 0.2.10 release manifest

0.2.10 feature/configuration changes:
- opens message-body links without an explicit target in a new tab/window instead of navigating inside the sandboxed mail-preview iframe; explicit targets remain intact
- shows the login success toast only after a real POST login; session restoration/page refresh is silent
- improves non-ASCII/Polish mail display with explicit UTF-8 preview documents and broader RFC 2047 header decoding (including ISO-8859-2/Windows-1250)
- previews PDFs from the authenticated inline attachment endpoint instead of a blob iframe for Safari/iPhone compatibility
- presents compose attachment/message size limits as compact raw values without implementation-detail descriptions
- retains the 0.2.9 realtime notification, shortcut and 300-message mailbox behavior
- requires no runtime schema migration; V049 remains next
Architecture:
- database_backend = sqlite | mysql | pgsql selects authoritative SQL only
- blob storage and search are independent from the SQL engine
- PostgreSQL/MySQL single-node deployments may continue to use data_dir-backed filesystem/Tantivy
- cluster mode clears an implicit/default data_dir; explicit data_dir is not forbidden, but local-only capabilities are rejected

Blob storage:
- filesystem: local single-node or shared POSIX with storage.shared=true
- shared POSIX examples: NFS, CephFS, GlusterFS
- s3: AWS S3 and S3-compatible endpoints such as MinIO/Ceph RGW
- attachment rows use logical storage keys and SHA-256 metadata
- storage migration command: rustbox storage migrate --from filesystem:/path --to configured [--dry-run] [--verify]

Search:
- local_tantivy: single-node only
- opensearch: cluster-capable external index
- disabled: no full-text index
- OpenSearch operations are tenant-scoped by user_hash
- durable SQL outbox provides claim/lease, retry/backoff and dead-letter handling
- rebuild command: rustbox search reindex

Database/schema:
- migrations/{sqlite,mysql,pgsql}/schema.sql contain the current fresh schema
- compatibility baseline remains V046
- runtime migration V047 adds attachment checksum metadata and search_outbox
- runtime migration V048 adds `folders.counter_generation` for race-safe authoritative IMAP counter writes
- next migration number: V049

Docker examples:
- docker/compose-single-sqlite.yml
- docker/compose-ha-garage.yml (2x RustBox + Envoy + Valkey + PostgreSQL + OpenSearch + Garage S3)
- docker/compose-postgres-s3-opensearch.yml (PostgreSQL + SILO/S3 + OpenSearch)
- docker/compose-mysql-nfs-opensearch.yml (MySQL + real NFS volume + OpenSearch)

Operations/docs:
- README.md documents 0.2.10 configuration
- docker/README.md documents Compose variants
- docs/STORAGE_SEARCH_OPERATIONS.md documents failure modes, shared-storage requirements and migration behavior
- TODO.md leaves live SILO/MinIO/AWS/Ceph and real multi-node acceptance validation explicitly pending

Build/release metadata:
- `scripts/package-release.sh` runs the full Rust release gate before creating ZIP/SHA256 artifacts
- Cargo.toml version = 0.2.10
- rust-toolchain.toml pins Rust 1.99.1
- Cargo.lock is retained for reproducible application builds; the release gate generates it only when missing
- CI and scripts/build-release.sh use the retained Cargo.lock (generating it only if missing), then run locked tests/Clippy/release build