Prepare network_system for v1.0 release

[kcenon]

What

Prepare network_system for a stable v1.0 release. Tier 4 library — depends on all Tier 0-3 libraries.

• Current version: 0.1.1
• Test coverage: 40% (critical gap — must reach 70%+)
• API stability: Low (Result migration in progress)

Part of kcenon/common_system#639

Why

• Provides networking layer for pacs_system (the top-tier application)
• Test coverage at 40% is the lowest in the ecosystem — major blocker for v1.0
• Result<T> migration is actively in progress — must complete before API freeze
• This is the most work-intensive v1.0 preparation in the ecosystem

How

v1.0 Readiness Checklist

• Test coverage: Increase from 40% to 70%+ minimum (see Expand unit test coverage from 40% to 80% #953)
• Result<T> migration: Complete migration, zero throw in public APIs (see Complete Result<T> migration in bridge/adapter implementations #957)
• API freeze audit: Review all public headers — no breaking changes after freeze
• CMake exports: Stable target name network_system::network_system
• Deprecation cleanup: Remove any deprecated APIs
• Documentation: Complete API reference and migration guide from 0.x
• CHANGELOG: Ensure keep-a-changelog format
• Semantic versioning: Tag v1.0.0 release

Dependencies

• Blocked by: common_system v1.0 (Prepare common_system for v1.0 release common_system#640)
• Blocked by: thread_system v1.0 (Prepare thread_system for v1.0 release thread_system#670)
• Blocked by: logger_system v1.0 (Prepare logger_system for v1.0 release logger_system#604)
• Blocked by: monitoring_system v1.0
• Blocked by: database_system v1.0
• Related: Expand unit test coverage from 40% to 80% #953 (test coverage improvement)
• Related: Complete Result<T> migration in bridge/adapter implementations #957 (Result<T> migration)

Acceptance Criteria

• Test coverage at 70%+ (from current 40%)
• Result<T> migration fully complete
• All public API headers reviewed and frozen
• No throw statements in public API paths
• CMake find_package(network_system) works cleanly
• Full test suite passes
• README documents v1.0 API guarantees