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/services/git_service.py

@@ -1,6 +1,6 @@
 # [DEF:backend.src.services.git_service:Module]
 #
-# @TIER:      STANDARD
+# @COMPLEXITY: 3
 # @SEMANTICS: git, service, gitpython, repository, version_control
 # @PURPOSE:   Core Git logic using GitPython to manage dashboard repositories.
 # @LAYER:     Service
@@ -32,7 +32,7 @@ from src.models.config import AppConfigRecord
 from src.core.database import SessionLocal
 
 # [DEF:backend.src.services.git_service.GitService:Class]
-# @TIER: STANDARD
+# @COMPLEXITY: 3
 # @PURPOSE: Wrapper for GitPython operations with semantic logging and error handling.
 class GitService:
     """