Add DB version indicator for sync status visibility

Description: When syncing a vault across devices, there's currently no way to tell which copy is more up-to-date. Please consider adding a short version hash or monotonic counter to each local database — similar to a git commit short SHA (e.g. aa09276) or a lamport timestamp.

This would allow users to:

• visually confirm which device holds the latest vault state

• detect sync conflicts before they cause data loss

• have confidence the sync actually completed successfully

Suggested display: A small indicator in the vault/sync settings screen, e.g.:

Vault: MyPasswords
DB version: a3f91bc · Last synced: 2 min ago

Alternative approaches worth considering:

• Monotonic counter — simpler (v1042), increments on every write, easy to compare

• Content hash (SHA of the full DB) — precise but slightly heavier

• Logical timestamp — e.g. ISO 8601 of last write, no extra infra needed

Any of these would significantly improve sync confidence for power users.