Closes #672
Part of #670

Summary

• Attach [[deprecated]] attributes to legacy thread_logger user-facing methods (log, log_error, set_level, set_enabled, set_lightweight_mode, is_lightweight_mode) so consumers of the legacy logging path see compiler warnings. Internal SDOF-safe helpers (instance, is_shutting_down, prepare_shutdown) remain stable because thread_context still depends on them.
• Emit #pragma message warnings on include of compatibility.h (namespace aliases thread_system, thread_module, thread_namespace, utility_module) and lockfree/lockfree_queue.h (forwarding header for concurrent_queue.h). Namespace aliases cannot carry a portable [[deprecated]] attribute, so pragma-based warnings are the only viable signal.
• Provide suppression macros (THREAD_SUPPRESS_LEGACY_NAMESPACE_WARNING, THREAD_SUPPRESS_LEGACY_LOCKFREE_QUEUE_WARNING) for consumers that need a quiet migration window.
• queue.cppm defines THREAD_SUPPRESS_LEGACY_LOCKFREE_QUEUE_WARNING before including lockfree_queue.h so the module re-export path stays quiet.
• Add a v1.0.0 API Freeze section to docs/advanced/MIGRATION.md that records the frozen public surface, the legacy APIs scheduled for removal in v2.0.0, and the suppression macros consumers can use during migration.

Context

The v3.0.0 pass removed legacy types (thread::result<T>, result_void, error, logger_interface, monitoring_interface) but left transitional compatibility surfaces without compiler-visible deprecation signals. Issue #672 is the v1.0 freeze audit — surface-wide review of 129 public headers to add [[deprecated]] markers and migration paths before v2.0 can make breaking changes. No dead code was found; the freeze is additive only.

What changed

Test plan

• cmake --build build-debug succeeds with exit code 0
• Build emits 11 deprecation warnings from consumers that still touch the legacy methods — proves attributes are effective
• ctest --test-dir build-debug — 382/383 thread_base_unit tests pass (same pre-existing LifecycleControllerTest.InitialStateIsCreated failure as before Replace throw statements with Result<T> in public API #671; unrelated to this PR)
• No changes to functional behavior; only attribute/message additions and doc updates
• queue.cppm module re-export path stays quiet (suppression macro applied before include)

Notes for reviewers

• The log_level enum itself does not carry [[deprecated]]. Applying it at the enum level would trigger warnings inside thread_logger.h itself (member initializer, internal signatures, level_to_string). The deprecation still propagates because every user-facing method that accepts log_level is itself [[deprecated]]. The rationale is documented in the enum's doc comment.
• Namespace aliases (thread_system, thread_module, etc.) can't be marked [[deprecated]] in portable C++ — the standard permits the attribute on namespace definitions but not on aliases. #pragma message is the only portable fallback.
• v3.0.0 migration section in MIGRATION.md is preserved unchanged for historical context. The new v1.0.0 section is additive.