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/models/worklog.py

@@ -1,14 +1,22 @@
 """Worklog model — immutable internal time-tracking records."""
 
+# Import uuid
 import uuid
 
+# Import Column, DateTime, ForeignKey, Index, Integer, S... from sqlalchemy
 from sqlalchemy import Column, DateTime, ForeignKey, Index, Integer, String, Text, func
+
+# Import JSONB, UUID from sqlalchemy.dialects.postgresql
 from sqlalchemy.dialects.postgresql import JSONB, UUID
+
+# Import relationship from sqlalchemy.orm
 from sqlalchemy.orm import relationship
 
+# Import Base from app.database
 from app.database import Base
 
 
+# Define class Worklog
 class Worklog(Base):
     """Internal worklog entry with integrity hash for audit compliance.
 
@@ -17,25 +25,42 @@ class Worklog(Base):
     the immutable fields so tampering can be detected.
     """
 
+    # Assign __tablename__ = "worklogs"
     __tablename__ = "worklogs"
 
+    # Assign id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
     id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    # Assign entity_type = Column(String(50), nullable=False)
     entity_type = Column(String(50), nullable=False)
+    # Assign entity_id = Column(UUID(as_uuid=True), nullable=False)
     entity_id = Column(UUID(as_uuid=True), nullable=False)
+    # Assign user_id = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=False)
     user_id = Column(UUID(as_uuid=True), ForeignKey("users.id"), nullable=False)
+    # Assign activity_type = Column(String(100), nullable=False)
     activity_type = Column(String(100), nullable=False)
+    # Assign started_at = Column(DateTime, nullable=False)
     started_at = Column(DateTime, nullable=False)
+    # Assign ended_at = Column(DateTime)
     ended_at = Column(DateTime)
+    # Assign duration_seconds = Column(Integer, nullable=False)
     duration_seconds = Column(Integer, nullable=False)
+    # Assign description = Column(Text)
     description = Column(Text)
+    # Assign tempo_synced = Column(DateTime)
     tempo_synced = Column(DateTime)
+    # Assign tempo_worklog_id = Column(String(100))
     tempo_worklog_id = Column(String(100))
+    # Assign integrity_hash = Column(String(64))
     integrity_hash = Column(String(64))
+    # Assign created_at = Column(DateTime(timezone=True), server_default=func.now())
     created_at = Column(DateTime(timezone=True), server_default=func.now())
+    # Assign extra_metadata = Column("metadata", JSONB, default={})
     extra_metadata = Column("metadata", JSONB, default={})
 
+    # Assign user = relationship("User", foreign_keys=[user_id])
     user = relationship("User", foreign_keys=[user_id])
 
+    # Assign __table_args__ = (
     __table_args__ = (
         Index("ix_worklogs_entity_id", "entity_id"),
         Index("ix_worklogs_user_id", "user_id"),