feat: verify dataset compatibility and integrity

[xr843]

Summary

• validate dataset version, normalization protocol, required query schema, FTS5 trigram declaration, SQLite integrity, and external-content FTS consistency
• add fojin data verify with human and JSON output while keeping normal query connections read-only
• make data update download and fully validate an isolated candidate before atomically replacing live data
• preserve the live database or a validated Windows recovery candidate across every download, validation, and replacement failure path
• enforce the Rust 1.77 MSRV, locked installation, Windows data tests, and the four release targets in CI

Why

Previously, incompatible or internally inconsistent local data could fail only at query time, and data update removed the current database before a replacement was proven usable. The CLI also had no explicit health-check command.

User impact

fojin data verify now performs protocol, SQLite, and FTS checks without downloading data. Queries reject incompatible data before use. Updates preserve the current working dataset until a downloaded candidate passes all checks.

Validation

• cargo fmt --all --check
• cargo clippy --all-targets -- -D warnings
• cargo test --all --locked (95 tests)
• cargo +1.77.0 test --all --locked (95 tests)
• python3 -m pytest tests/ -q
• cargo build --release --locked
• Rust 1.77 locked cargo install --path .
• real 587,984,896-byte dataset: full SQLite + FTS verification passed
• independent whole-branch review: approved with no findings