Branchable temporal records with explainable history #359

Area: Database\Temporal, model queries, migrations

Problem

Doppar already supports querying temporal data at a point in time, but teams
cannot safely compare proposed changes, explain who changed a record, or revert
one version without manually copying rows.

Proposal

Extend temporal models with named branches, version diffs, and a guarded
restoreVersion() operation. Keep the existing temporal table format as the
default and make branch metadata opt-in.

Acceptance criteria

• A branch can be created from a selected timestamp and queried independently.
• Diffs identify changed attributes while respecting casts and hidden fields.
• Restoring a version creates a new version; it never rewrites history.
• SQLite, MySQL, and PostgreSQL behavior is covered where supported.

Make temporal persistence useful for business workflows, not only historical reads: history stays immutable and proposed state is safely reviewable.