feat(docs): Add comprehensive documentation for Vexer, Vulnerability Explorer, and Zastava modules

- Introduced AGENTS.md, README.md, TASKS.md, and implementation_plan.md for Vexer, detailing mission, responsibilities, key components, and operational notes.
- Established similar documentation structure for Vulnerability Explorer and Zastava modules, including their respective workflows, integrations, and observability notes.
- Created risk scoring profiles documentation outlining the core workflow, factor model, governance, and deliverables.
- Ensured all modules adhere to the Aggregation-Only Contract and maintain determinism and provenance in outputs.

docs/modules/advisory-ai/implementation_plan.md

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+# Implementation plan — Advisory AI
+
+## Current objectives
+- Deliver Epic milestones summarised below while maintaining determinism and offline parity.
+- Keep documentation, telemetry, and runbooks aligned with sprint outcomes.
+
+## Workstreams
+- Roadmap: reconcile open stories in ../../TASKS.md with module backlog.
+- Delivery: ship features outlined in the epic while preserving AOC guardrails.
+- Validation: extend tests/fixtures to guarantee reproducibility and provenance.
+
+## Epic milestones
+- Epic 8: Advisory AI Assistant.
+- DOCS-AI stories to be tracked in ../../TASKS.md.
+
+## Coordination
+- Review ./AGENTS.md before picking up work.
+- Sync with owners listed in docs/implplan/SPRINTS.md.
+- Update this plan whenever scope, dependencies, or guardrails change.