align database documentation with java-tron v4.8.2

[abn2357]

Align the database documentation with the database-related changes in java-tron v4.8.2.

Changes

• Lite snapshot balance exclusion: documented the --exclude-historical-balance option added to db lite split -t snapshot. The option excludes the balance-trace and account-trace databases to reduce snapshot size; the default behavior remains unchanged.
• Historical balance compatibility: documented that snapshots created with this option cannot safely serve historical balance queries when the source node has storage.balance.history.lookup = true, and that merging a history dataset does not restore the excluded databases.
• Lite FullNode guidance: added the option to the snapshot creation workflow and linked to the complete command and compatibility warning.
• Periodic RocksDB backups: documented that the storage.backup feature was removed in java-tron v4.8.2, existing settings are ignored, and java-tron no longer creates periodic database copies through this mechanism.

Test plan

• Verified every claim against the corresponding java-tron v4.8.2 PRs
• Confirmed mkdocs build --strict and git diff --check pass