feat(orm): add optional explicit soft-delete support

[GaspardKirira]

Summary

Allow repositories to mark entities as deleted instead of physically removing their rows.

Soft-delete behavior must be opt-in and visible in repository configuration.

Current behavior

removeById() and removeAll() always execute physical DELETE statements.

Applications requiring archival behavior must implement custom repositories.

Expected behavior

A repository configured with a soft-delete column must:

• update that column during removal;
• exclude deleted rows from normal reads;
• allow explicit access to deleted rows;
• allow restoration where supported.

Scope

• Define soft-delete metadata.
• Support boolean soft-delete columns.
• Support timestamp soft-delete columns.
• Apply the condition to read operations.
• Apply the condition to count and existence operations.
• Add explicit include-deleted options.
• Add restoration.
• Add SQLite integration tests.
• Preserve physical deletion for normal repositories.

Suggested files

• modules/orm/include/vix/orm/Repository.hpp
• modules/orm/include/vix/orm/SoftDelete.hpp
• modules/orm/tests/soft_delete_test.cpp

Acceptance criteria

• Soft delete is disabled by default.
• Configured removal updates the marker.
• Normal reads exclude deleted rows.
• Explicit reads can include deleted rows.
• Restoration clears the marker.
• Physical deletion remains available explicitly.
• Existing repositories remain unchanged.

Non-goals

This issue does not include:

• automatic data retention policies;
• scheduled cleanup;
• relationship cascading;
• audit history.

Suggested labels

• scope:orm
• type:feature
• tests
• help wanted
• status:accepted