feat(dashboard)[#254]: soft delete(archive) support for log sessions

[AaronProbha18]

Fixes: #254

Changes

• Added non-destructive soft delete support for dashboard sessions by introducing an archived flag in the session override metadata store.
• Implemented scanner-level archive lifecycle operations:
  • archive_session() to mark sessions as archived (without deleting .fn files)
  • restore_session() to unarchive sessions
  • archived-session filtering in listings, with opt-in inclusion support
• Added new authenticated, CSRF-protected API endpoints:
  • POST /api/session/<project>/<session>/archive
  • POST /api/session/<project>/<session>/restore
• Added archived-session query support (include_archived) for dashboard/API listing flows.
• Updated dashboard UI to:
  • Show Archive/Restore actions alongside existing rename/delete controls
  • Hide archived sessions by default and allow explicit archived visibility mode
  • Keep existing rename/delete interactions working with the new archive state
• Added tests for soft delete behavior, including scanner and API coverage.

Notes

• Soft delete is metadata-only: archiving does not modify or remove underlying .fn experiment log files.
• Archived state is persisted in the dashboard override store and can be toggled via restore at any time.
• Existing hard delete remains available for permanent removal when explicitly requested.
• Archived filtering now defaults to hidden unless include_archived=true is provided.

[ApusBerliozi]

Thx 4 your work mate!