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/detection_rule.py

@@ -1,39 +1,61 @@
 """DetectionRule model — detection rules from multiple sources."""
 
+# Import uuid
 import uuid
 
+# Import Boolean, Column, DateTime, Index, String, Text,... from sqlalchemy
 from sqlalchemy import Boolean, Column, DateTime, Index, String, Text, func
+
+# Import JSONB, UUID from sqlalchemy.dialects.postgresql
 from sqlalchemy.dialects.postgresql import JSONB, UUID
 
+# Import Base from app.database
 from app.database import Base
 
 
+# Define class DetectionRule
 class DetectionRule(Base):
-    """
-    Detection rule from an external source (Sigma, Elastic, Splunk, custom).
+    """Detection rule from an external source (Sigma, Elastic, Splunk, custom).
 
     Each rule is mapped to one MITRE ATT&CK technique via
     ``mitre_technique_id`` and stores the complete rule content in
     ``rule_content``.
     """
+    # Assign __tablename__ = "detection_rules"
     __tablename__ = "detection_rules"
 
+    # 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 mitre_technique_id = Column(String, nullable=False)            # e.g. "T1059.001"
     mitre_technique_id = Column(String, nullable=False)            # e.g. "T1059.001"
+    # Assign title = Column(String, nullable=False)
     title = Column(String, nullable=False)
+    # Assign description = Column(Text, nullable=True)
     description = Column(Text, nullable=True)
+    # Assign source = Column(String, nullable=False)                        # sigma / ela...
     source = Column(String, nullable=False)                        # sigma / elastic / splunk / custom
+    # Assign source_id = Column(String, nullable=True)                      # ID in the sour...
     source_id = Column(String, nullable=True)                      # ID in the source repo (for dedup)
+    # Assign source_url = Column(String, nullable=True)
     source_url = Column(String, nullable=True)
+    # Assign rule_content = Column(Text, nullable=False)                    # YAML / KQL / SPL ...
     rule_content = Column(Text, nullable=False)                    # YAML / KQL / SPL content
+    # Assign rule_format = Column(String, nullable=False)                   # sigma_yaml / kql...
     rule_format = Column(String, nullable=False)                   # sigma_yaml / kql / spl / custom
+    # Assign severity = Column(String, nullable=True)                       # informational...
     severity = Column(String, nullable=True)                       # informational / low / medium / high / critical
+    # Assign platforms = Column(JSONB, nullable=True, default=[])
     platforms = Column(JSONB, nullable=True, default=[])
+    # Assign log_sources = Column(JSONB, nullable=True)                     # e.g. {"product":...
     log_sources = Column(JSONB, nullable=True)                     # e.g. {"product": "windows", "service": "sysmon"}
+    # Assign false_positive_rate = Column(String, nullable=True)            # low / medium / high
     false_positive_rate = Column(String, nullable=True)            # low / medium / high
+    # Assign is_active = Column(Boolean, default=True)
     is_active = Column(Boolean, default=True)
+    # Assign created_at = Column(DateTime(timezone=True), server_default=func.now())
     created_at = Column(DateTime(timezone=True), server_default=func.now())
 
+    # Assign __table_args__ = (
     __table_args__ = (
         Index('ix_detection_rules_mitre_technique_id', 'mitre_technique_id'),
         Index('ix_detection_rules_source', 'source'),