Gate incompatible alpha wallet databases

[czarcas7ic]

Summary

• Add an early wallet SQLite compatibility gate before WalletMigrator can mutate an existing database.
• Add Zallet-owned compatibility epoch metadata and record epoch 1 after a successful open/migration.
• Reject legacy alpha databases whose latest recorded Zallet version is older than 0.1.0-alpha.4, while preserving the existing network mismatch error path.
• Treat recorded compatibility epochs as exact-match only, so older binaries fail closed if a database was touched by a newer alpha.

Context

• This is for the upstream alpha.4 wallet DB compatibility issue. This fork draft is for CI and review; the eventual upstream PR should include the repository-local closing reference for upstream issue 264.

Validation

• First added the alpha.3 fixture regression test and confirmed it failed before the compatibility gate because the database opened successfully.
• Added regression coverage that rejects future compatibility epochs.
• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test -p zallet components::database::tests --all-features
• env -u RUST_LOG cargo test --workspace --all-features