refactor(compat): add container namespace migration infrastructure (Issue #224)

[kcenon]

Closes #224

Summary

• Created centralized container_aliases.h for the upcoming container_module -> kcenon::container namespace migration
• Completed Phase 1 (audit) and Phase 2 (migration infrastructure) of the issue scope
• Phase 3 (actual namespace replacement) remains blocked until container_system v2.0 enforces the new namespace

Phase 1: Audit Results

Pattern	Count	Files
container_module:: (total)	368	46 .h/.cpp files
container_module:: (modules)	16	2 .cppm files
container_module::value_container	365	45 files
container_module::value_types	1	1 file
#include <core/container.h>	4	4 header files
container_module::value_variant	0	0 files
container_module::serialization_format	0	0 files
value_container_ptr (deprecated)	0	0 files

Total: ~384 references across 48 files

Phase 2: Migration Infrastructure

New file: include/kcenon/messaging/compat/container_aliases.h

Provides centralized aliases:

namespace kcenon::messaging::compat {
    namespace container_ns = container_module;  // -> kcenon::container
    using container_data = container_ns::value_container;  // -> message_buffer
    using container_data_ptr = std::shared_ptr<container_data>;
    using container_value_types = container_ns::value_types;
}

Migration Strategy

When container_system v2.0 enforces the new namespace:

1. Update container_aliases.h: change container_module -> kcenon::container
2. Update container_aliases.h: change value_container -> message_buffer
3. Incrementally replace container_module:: references with aliases across codebase (Phase 3)

Phase 3: Blocked

• Requires container_system v2.0 namespace enforcement
• Will involve replacing 384 references across 48 files
• Tracked as remaining tasks in Issue [Refactor] Prepare for container_module to kcenon::container namespace migration #224

Test Plan

• New header compiles without errors (header-only, includes <core/container.h>)
• No existing code modified (zero regression risk)
• CI build passes on all platforms