feat(dashboard): Phase 13 — Executive Dashboard

PostureSnapshot model, Alembic migration (b039exec), schemas, service
aggregating all phases (coverage/risk/operations/knowledge/MTTD), and
router at /api/v1/dashboard with executive view, KPIs, coverage-by-tactic,
posture-history, posture-snapshot, and activity-feed endpoints.

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

backend/app/models/executive_dashboard.py

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+"""Phase 13: Executive Dashboard — PostureSnapshot model."""
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import (
+    Boolean, Column, Date, DateTime, Float, ForeignKey,
+    Index, Integer, UniqueConstraint,
+)
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from app.database import Base
+
+
+class PostureSnapshot(Base):
+    """
+    Daily point-in-time capture of the organisation's security posture.
+
+    Aggregates data from all phases (coverage, risk, ownership, knowledge,
+    attack-paths) into a single row that can be trended over time.
+    """
+
+    __tablename__ = "posture_snapshots"
+
+    id             = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    snapshot_date  = Column(Date, nullable=False)    # one per calendar day
+
+    # ── Coverage ──────────────────────────────────────────────────────────────
+    total_techniques  = Column(Integer, nullable=False, default=0)
+    validated_count   = Column(Integer, nullable=False, default=0)
+    partial_count     = Column(Integer, nullable=False, default=0)
+    not_covered_count = Column(Integer, nullable=False, default=0)
+    coverage_pct      = Column(Float, nullable=False, default=0.0)  # 0–100
+
+    # ── Risk ─────────────────────────────────────────────────────────────────
+    avg_risk_score     = Column(Float, nullable=False, default=0.0)
+    critical_count     = Column(Integer, nullable=False, default=0)
+    high_count         = Column(Integer, nullable=False, default=0)
+    medium_count       = Column(Integer, nullable=False, default=0)
+    low_count          = Column(Integer, nullable=False, default=0)
+
+    # ── Operations ────────────────────────────────────────────────────────────
+    open_queue_items   = Column(Integer, nullable=False, default=0)
+    orphan_techniques  = Column(Integer, nullable=False, default=0)
+
+    # ── Knowledge ─────────────────────────────────────────────────────────────
+    playbook_count     = Column(Integer, nullable=False, default=0)
+    lesson_count       = Column(Integer, nullable=False, default=0)
+
+    # ── MTTD (from attack-path executions completed in last 30 d) ────────────
+    mttd_avg_seconds   = Column(Float, nullable=True)     # None if no data
+    executions_30d     = Column(Integer, nullable=False, default=0)
+    detection_rate_30d = Column(Float, nullable=True)     # avg across executions
+
+    # ── Meta ─────────────────────────────────────────────────────────────────
+    created_by  = Column(
+        UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True
+    )
+    created_at  = Column(DateTime, default=datetime.utcnow)
+    extra       = Column(JSONB, nullable=True)   # full breakdown / by-tactic
+
+    creator = relationship("User", foreign_keys=[created_by])
+
+    __table_args__ = (
+        UniqueConstraint("snapshot_date", name="uq_posture_snapshot_date"),
+        Index("ix_posture_snapshots_date", "snapshot_date"),
+    )