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/schemas/executive_dashboard_schema.py

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+"""Phase 13: Executive Dashboard — Pydantic schemas."""
+
+from __future__ import annotations
+
+from datetime import date, datetime
+from typing import Any, Dict, List, Optional
+from uuid import UUID
+
+from pydantic import BaseModel, Field
+
+
+class PostureSnapshotOut(BaseModel):
+    id:              UUID
+    snapshot_date:   date
+
+    # Coverage
+    total_techniques:   int
+    validated_count:    int
+    partial_count:      int
+    not_covered_count:  int
+    coverage_pct:       float
+
+    # Risk
+    avg_risk_score:  float
+    critical_count:  int
+    high_count:      int
+    medium_count:    int
+    low_count:       int
+
+    # Operations
+    open_queue_items:   int
+    orphan_techniques:  int
+
+    # Knowledge
+    playbook_count:  int
+    lesson_count:    int
+
+    # MTTD
+    mttd_avg_seconds:    Optional[float] = None
+    executions_30d:      int
+    detection_rate_30d:  Optional[float] = None
+
+    # Meta
+    created_by: Optional[UUID] = None
+    created_at: Optional[datetime] = None
+    extra:      Optional[Dict[str, Any]] = None
+
+    class Config:
+        from_attributes = True
+
+
+class ExecutiveSummary(BaseModel):
+    """Full executive view — current posture + trends."""
+    snapshot:          PostureSnapshotOut
+    coverage_trend:    List[Dict[str, Any]] = Field(
+        default_factory=list,
+        description="Last 30-day coverage_pct series [{date, value}]",
+    )
+    risk_trend:        List[Dict[str, Any]] = Field(
+        default_factory=list,
+        description="Last 30-day avg_risk_score series [{date, value}]",
+    )
+    top_risks:         List[Dict[str, Any]] = Field(
+        default_factory=list,
+        description="Top 5 highest-risk techniques",
+    )
+    coverage_by_tactic: List[Dict[str, Any]] = Field(
+        default_factory=list,
+        description="Per-tactic validated/partial/not_covered counts",
+    )
+    recent_activity:   List[Dict[str, Any]] = Field(
+        default_factory=list,
+        description="Most-recent events (tests, paths, queue changes)",
+    )
+
+
+class KpiBlock(BaseModel):
+    """Compact KPI block for a dashboard header."""
+    coverage_pct:        float
+    avg_risk_score:      float
+    critical_count:      int
+    open_queue_items:    int
+    orphan_techniques:   int
+    mttd_avg_seconds:    Optional[float] = None
+    detection_rate_30d:  Optional[float] = None
+    playbook_count:      int
+    lesson_count:        int
+    snapshot_date:       date
+    snapshot_id:         UUID
+
+
+class CoverageByTactic(BaseModel):
+    tactic:        str
+    total:         int
+    validated:     int
+    partial:       int
+    not_covered:   int
+    coverage_pct:  float
+
+
+class PostureHistoryEntry(BaseModel):
+    snapshot_date:   date
+    coverage_pct:    float
+    avg_risk_score:  float
+    critical_count:  int
+    open_queue_items: int
+
+
+class ActivityEntry(BaseModel):
+    ts:       datetime
+    category: str      # "test" | "attack_path" | "queue" | "osint"
+    title:    str
+    detail:   Optional[str] = None