feat(phase-38): automatic intelligence — OSINT enrichment + stale coverage detection

Tarea 4.1 — OSINT Enrichment:
- Add OsintItem model with source_type, severity, CVSS metadata, review flag
- Add Alembic migration b022 with osint_items table and optimized indexes
- Add osint_enrichment_service with NVD API integration, deduplication, rate limiting
- Add OSINT router: GET /osint/items, /osint/summary, /osint/technique/{id}
- Add POST /osint/items/{id}/review to mark items as reviewed
- Add POST /osint/enrich/{technique_id} for manual single-technique enrichment
- Techniques with new CVEs are automatically flagged review_required=True
- Register weekly enrichment job in APScheduler
- Add NVD_API_KEY config setting for optional increased rate limits

Tarea 4.2 — Stale Coverage Detection:
- Add stale_detection_service that flags techniques with no validated test
  in the last N days, or never-validated but with a coverage status
- Configurable threshold via STALE_THRESHOLD_DAYS setting (default 365)
- Register daily stale detection job in APScheduler
- Only flags techniques not already marked review_required

backend/alembic/versions/b022_add_osint_items.py

@@ -0,0 +1,47 @@
+"""add_osint_items
+
+Revision ID: b022osintitems
+Revises: b021phasetiming
+Create Date: 2026-02-17 22:00:00.000000
+
+Add osint_items table for OSINT enrichment data linked to techniques.
+"""
+
+from alembic import op
+
+revision = "b022osintitems"
+down_revision = "b021phasetiming"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.execute("""
+        CREATE TABLE IF NOT EXISTS osint_items (
+            id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+            technique_id UUID NOT NULL REFERENCES techniques(id),
+            source_type  VARCHAR(50)  NOT NULL,
+            source_url   TEXT         NOT NULL,
+            title        VARCHAR(500) NOT NULL,
+            description  TEXT,
+            severity     VARCHAR(20),
+            discovered_at TIMESTAMP   NOT NULL DEFAULT now(),
+            reviewed     BOOLEAN      NOT NULL DEFAULT false,
+            metadata     JSONB        DEFAULT '{}'::jsonb
+        );
+
+        CREATE INDEX IF NOT EXISTS ix_osint_items_technique_id
+            ON osint_items (technique_id);
+
+        CREATE INDEX IF NOT EXISTS ix_osint_items_source_type
+            ON osint_items (source_type);
+
+        CREATE INDEX IF NOT EXISTS ix_osint_items_reviewed
+            ON osint_items (reviewed) WHERE NOT reviewed;
+    """)
+
+
+def downgrade() -> None:
+    op.execute("""
+        DROP TABLE IF EXISTS osint_items CASCADE;
+    """)