Context

Part of kcenon/common_system#685 (Wave 1, P0). Code-structure reference: monitoring_system.

Problem (P0, audit-blocking)

• include path is include/kcenon/database/ but internal namespace is database:: (133 uses) -> consumer using confusion
• legacy_include/database/ parallel forwarding tree is also installed (both <database/...> and <kcenon/database/...> exported)
• src root holds loose *_manager.cpp files

Acceptance Criteria

• namespace migrated to kcenon::database:: (compat alias retained, tracked)
• legacy_include/ removed from install or given an explicit deprecation/removal version
• loose src manager files relocated into domain folders

Derived from the 2026-05-30 multi-agent cross-system level-matching analysis (workflow wf_0a968699-e07). Reference systems: documentation=common_system, code-structure=monitoring_system, tests/examples=container_system.