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.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/evidence.py

@@ -1,34 +1,53 @@
 """Pydantic schemas for Evidence endpoints."""
 
+# Import uuid
 import uuid
+
+# Import datetime from datetime
 from datetime import datetime
 
+# Import BaseModel, ConfigDict from pydantic
 from pydantic import BaseModel, ConfigDict
 
+# Import TeamSide from app.models.enums
 from app.models.enums import TeamSide
 
 
+# Define class EvidenceOut
 class EvidenceOut(BaseModel):
     """Representation of an evidence record returned by the API.
 
     ``download_url`` is a presigned URL generated at response time.
     """
 
+    # id: uuid.UUID
     id: uuid.UUID
+    # test_id: uuid.UUID
     test_id: uuid.UUID
+    # file_name: str
     file_name: str
+    # sha256_hash: str
     sha256_hash: str
+    # Assign uploaded_by = None
     uploaded_by: uuid.UUID | None = None
+    # Assign uploaded_at = None
     uploaded_at: datetime | None = None
+    # Assign team = TeamSide.red
     team: TeamSide = TeamSide.red
+    # Assign notes = None
     notes: str | None = None
+    # Assign download_url = None
     download_url: str | None = None
 
+    # Assign model_config = ConfigDict(from_attributes=True)
     model_config = ConfigDict(from_attributes=True)
 
 
+# Define class EvidenceUpload
 class EvidenceUpload(BaseModel):
     """Metadata sent alongside an evidence file upload."""
 
+    # team: TeamSide
     team: TeamSide
+    # Assign notes = None
     notes: str | None = None