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/config.py

@@ -1,6 +1,6 @@
 # [DEF:backend.src.models.config:Module]
 #
-# @TIER: CRITICAL
+# @COMPLEXITY: 5
 # @SEMANTICS: database, config, settings, sqlalchemy, notification
 # @PURPOSE: Defines SQLAlchemy persistence models for application and notification configuration records.
 # @LAYER: Domain