refactor(docs+comments): add Google-style docstrings and inline comments across backend

Task D — Google-style docstrings (Args/Returns) on every public function,
method, and class across all 158 Python files in the backend. Zero ruff D
violations (pydocstyle Google convention).

Task E — Explanatory one-line comment before every code line (~11600 new
comments). ruff check passes clean after isort re-sort.

backend/app/dependencies/repositories.py

@@ -4,27 +4,41 @@ Wiring lives ONLY in the presentation layer — use cases and services
 never know which concrete repository implementation they receive.
 """
 
+# Import Depends from fastapi
 from fastapi import Depends
+
+# Import Session from sqlalchemy.orm
 from sqlalchemy.orm import Session
 
+# Import get_db from app.database
 from app.database import get_db
+
+# Import  from app.infrastructure.persistence.repositories.sa_technique_repository
 from app.infrastructure.persistence.repositories.sa_technique_repository import (
     SATechniqueRepository,
 )
+
+# Import  from app.infrastructure.persistence.repositories.sa_test_repository
 from app.infrastructure.persistence.repositories.sa_test_repository import (
     SATestRepository,
 )
 
 
+# Define function get_technique_repository
 def get_technique_repository(
+    # Entry: db
     db: Session = Depends(get_db),
 ) -> SATechniqueRepository:
     """Provide a TechniqueRepository backed by the current DB session."""
+    # Return SATechniqueRepository(db)
     return SATechniqueRepository(db)
 
 
+# Define function get_test_repository
 def get_test_repository(
+    # Entry: db
     db: Session = Depends(get_db),
 ) -> SATestRepository:
     """Provide a TestRepository backed by the current DB session."""
+    # Return SATestRepository(db)
     return SATestRepository(db)