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/registry/implementation_plan.md

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+# Implementation plan — Registry Token Service
+
+## Current objectives
+- Maintain deterministic behaviour and offline parity across releases.
+- Keep documentation, telemetry, and runbooks aligned with the latest sprint outcomes.
+
+## Workstreams
+- Backlog grooming: reconcile open stories in ../../TASKS.md with this module's roadmap.
+- Implementation: collaborate with service owners to land feature work defined in SPRINTS/EPIC docs.
+- Validation: extend tests/fixtures to preserve determinism and provenance requirements.
+
+## Epic milestones
+- **Epic 10 – Export Center:** deliver signed registry token bundles supporting mirror/Offline Kit workflows.
+- **Epic 14 – Identity & Tenancy:** integrate tenant-aware scope validation, revocation, and audit trails.
+- Track follow-ups in ../../TASKS.md and src/Registry/TASKS.md.
+
+## Coordination
+- Review ./AGENTS.md before picking up new work.
+- Sync with cross-cutting teams noted in ../../implplan/SPRINTS.md.
+- Update this plan whenever scope, dependencies, or guardrails change.