refactor(semantics): migrate legacy @TIER to @COMPLEXITY annotations

- Replaced @TIER: TRIVIAL with @COMPLEXITY: 1
- Replaced @TIER: STANDARD with @COMPLEXITY: 3
- Replaced @TIER: CRITICAL with @COMPLEXITY: 5
- Manually elevated specific critical/complex components to levels 2 and 4
- Ignored legacy, specs, and node_modules directories
- Updated generated semantic map

backend/tests/test_task_manager.py

@@ -1,5 +1,5 @@
 # [DEF:test_task_manager:Module]
-# @TIER: CRITICAL
+# @COMPLEXITY: 5
 # @SEMANTICS: task-manager, lifecycle, CRUD, log-buffer, filtering, tests
 # @PURPOSE: Unit tests for TaskManager lifecycle, CRUD, log buffering, and filtering.
 # @LAYER: Core