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/src/models/__tests__/test_models.py

@@ -1,5 +1,5 @@
 # [DEF:test_models:Module]
-# @TIER: TRIVIAL
+# @COMPLEXITY: 1
 # @PURPOSE: Unit tests for data models
 # @LAYER: Domain
 # @RELATION: VERIFIES -> src.models

backend/src/models/__tests__/test_report_models.py

@@ -1,5 +1,5 @@
 # [DEF:test_report_models:Module]
-# @TIER: STANDARD
+# @COMPLEXITY: 3
 # @PURPOSE: Unit tests for report Pydantic models and their validators
 # @LAYER: Domain
 # @RELATION: TESTS -> backend.src.models.report