Summary

Adopt unified KCENON_* feature flags and remove local __has_include checks in thread_system.

5W1H Specification

• Who: thread_system maintainers
• What: Replace THREAD_HAS_* detection with KCENON_HAS_*
• Where: thread_pool / typed_thread_pool headers
• When: TBD
• Why: Remove duplicated detection logic and align integration gates
• How: Include feature_flags header and update macros

Parent Issue

kcenon/common_system#223

Tasks

• Include kcenon/common/config/feature_flags.h (guarded if needed)
• Replace THREAD_HAS_COMMON_EXECUTOR / THREAD_HAS_COMMON_RESULT with KCENON_*
• Remove local __has_include based macro definitions
• Update docs to reference KCENON_* as primary flags

Acceptance Criteria

• No local __has_include-based macro definitions remain
• Integration behavior matches current builds