feat: Add sovereign tool stack and integrate ASTRAL/AOC across playbooks

New document: Sovereign Tool Stack — complete capability map for our
open-source consulting arsenal.

Documents updated:
- sovereign-tool-stack.md (new): Maps Prowler, BloodHound, CISO Assistant,
  Purple Knight/Forest Druid, ASTRAL, and AOC to engagement modules and
  antifragile pillars. Identifies 6 gaps with recommended closes:
  Wazuh+Sysmon (EDR), Shuffle (SOAR), TheHive+Cortex (case management),
  Cartography (cloud asset mapping), Syft+Grype+Trivy (containers),
  Zeek+Suricata (network analysis). Includes per-module tool pairing,
  deployment complexity matrix, and integration architecture.
- m365-e3-hardening.md: Added ASTRAL 'configuration immunity' section
  and AOC audit log integration references
- endpoint-management-entry-vector.md: Added ASTRAL for Intune
  configuration backup and drift detection
- modular-engagements.md: Added ASTRAL and AOC to Module 1/2/3
  deliverables; linked sovereign tool stack
- retained-capability.md: Added AOC and Wazuh to detection engineering
  description
- ai-assisted-tvm.md: Added AOC and Prowler to discovery layer table
- blue-purple-team-foundation.md: Added sovereign tool stack reference
  for open-source SOC architecture
- zero-budget-hardening.md: Linked sovereign tool stack
- README.md + index.md: Added sovereign-tool-stack.md to navigation

antifragile-consulting/core/blue-purple-team-foundation.md

@@ -120,6 +120,8 @@ Many organizations have purchased or inherited an impressive security stack:
 **For MSSP clients**: The first hunt often reveals gaps in MSSP detection coverage. These gaps become the first custom detection rules the retained capability cell writes and deploys.
 
 **Deliverable**: Operating Rhythm Playbook
+
+**Tool stack for the operating rhythm**: See the [Sovereign Tool Stack](../playbooks/sovereign-tool-stack.md) for the complete open-source SOC architecture. For M365-centric environments, AOC provides audit log intelligence; Wazuh + Sysmon provide endpoint detection; TheHive + Cortex provide case management; Shuffle provides automated response. This stack replaces €200K+/year commercial SOC tooling for clients who prioritise sovereignty.
 - Weekly, bi-weekly, and monthly cadence definitions
 - RACI matrix for each activity
 - Dashboard definitions and data sources